freedreno, turnip: Clarify some RB_CCU_CNTL fields

freedreno, turnip: Clarify some RB_CCU_CNTL fields

There is no .gmem field, there is a ccu color cache size field
which tells the size as a fraction of depth cache used in direct
rendering.

There is also GMEM_FAST_CLEAR_DISABLE flag which is set on a608/a610.

Since these values will stop being the same between models,
make them configurable.

Credits to Connor Abbott for deciphering color cache size meaning.

Signed-off-by: Danylo Piliaiev <dpiliaiev@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20991>