radeonsi: split si_shader_key into ps and ge parts to minimize memcmp overhead

radeonsi: split si_shader_key into ps and ge parts to minimize memcmp overhead

ps is for the pixel shader, while ge is for VS, TCS, TES, and GS.

si_shader_key: 68 bytes
si_shader_key_ge: 68 bytes
si_shader_key_ps: 28 bytes

The only notable change is that si_shader_select_with_key is changed
to a C++ template. Other changes are trivial.

Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13285>