[platform] - add info bools to determine the arch of the compilation

Basically as RFC. This adds the bool conditions:

system.arch.x86_32, x86_64, arm_32, arm_64, mips_32, mips_64

I added this to determine which libboblight.so i need to download (atm i only can determine android which defaults to arm atm - but at one point i need to distinguish between android-arm and android-x86) in the boblight addon.

This allows a python script to determine the compiled arch by something like

if xbmc.getCondVisibility('system.arch.mips_64'):
  downloadmips64lib()