Few source-code improvements

* Fixed identation inconsistency after last merge.
* Replaced uint32_t with u32 in LinearToSwizzleAddress.
* Replaced hardcoded values with defined GCM constants (in Emu/GS/GCM.h)
in some switch statements.

This commit won't produce any changes in the RPCS3 executable. It's just
to make the code easier to read.