gallium: whitespace, comment formatting fixes in p_defines.h
gallium: whitespace, comment formatting fixes in p_defines.h

Just to keep things consistent.

Reviewed-by: José Fonseca <61b5a29db2c0650f7c8510f93eece059c1b09320@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler