I am aware that holding a weapon with 2 hands allows you to use 1.5 of strength modifier for its damage dealt. If one would wield a weapon with more than 2 arms, like 4 or 6 would it provide some bonuses?
Pathfinder, so far as I'm aware, makes no mention of wielding a weapon with more than two hands. (Presumably, a 3-handed creature, for example, could wield a weapon with all three of its hands if it wanted to, but it wouldn't receive any particular advantage for doing so.)
However, in Pathfinder's antecedent Dungeons & Dragons 3.5 rules for three-or-more-handed wielding are available in Savage Species in a section with the on-the-nose title Three or More Hands:
[W]hen you deal damage with a weapon that you are wielding two-handed, you add 1 1/2 times your Strength bonus. The wielder of a light weapon does not get this higher Strength bonus when using the weapon two-handed…. Provided that a weapon is designed for more than two hands, each additional hand used increases the damage dealt with that weapon. Each hand used beyond the first adds 1/2 the wielder’s Strength bonus to the damage. A creature wielding a Medium-size longsword with two hands adds 1 1/2 times its Strength bonus to the damage roll. A girallon wielding a Huge club with all four hands adds 2 1/2 times its Strength bonus to the damage roll.
Any weapon… can be lengthened, balanced, and otherwise designed and crafted for creatures with more than two hands. The determining factor is the relationship between the size of the wielder and the size of the user. Light weapons can never be designed for use with more than two hands. One-handed weapons can already be used with two hands, and can be designed for use with four hands. Two-handed weapons can be designed for use with up to eight hands. The cost is for a masterwork version of the weapon, and the wielder gains the benefits of using a masterwork weapon as well. (42 and emphasis mine)
Thus, for example, a marilith could wield in its six hands a specially-designed greatsword and deal with it an extra 3½× the marilith's Strength bonus in addition to the weapon's normal damage. (Note that because of its extraordinary ability multiweapon mastery, this is usually a suboptimal choice for a marilith!)
With the GM's approval, this rule can ported largely as-is into Pathfinder, which is backwards-compatible with D&D 3.5. In the interest of full disclosure, I've used this rule in my D&D 3.5 campaigns and haven't found it to be unbalanced there, but I've not seen it used in a Pathfinder campaign, and, although I can't think of anything off hand, it's always possible that somewhere in the tens of thousands of pages of Pathfinder material that there's something that exploits ruthlessly this rule.
Short answer: No.
There may be a third party supplement out there that has a racial ability or feat to do so but none that I am aware of.
The rules as stated make sense.
The benefit that a humanoid gets from using two hands is that they are using their whole body to power the weapon.
So, if it takes more arms to transfer the whole body's power into the swing, it is still just the 1.5x increase from putting the whole body behind the swing.
I the argument is that something big enough to have that many arms would have more power, that is already counted in the increased STR from their size.