X Motor mount for TronXY P802M

I adapted the "X Motor mount for Anet A8 by Simhopp" to fit the dimensions of the TronXY P802M. Changes:

* Distance between z-axes rods: 17mm
* Distance between X-axes rods: 44mm
* Different z-endstop mount
* Different x-endstop mount

I also changed the x-belt tightener to another design. You **need** the green part http://www.thingiverse.com/thing:2102177, too. Other tighteners for the A8 will not fit because the smaller x-rod distance which forces the belt channel to be smaller, too.