mesa: Add new variables in gl_context to store sample layout

SampleMap{2,4,8}x variables are used in later patches to implement
EXT_framebuffer_multisample_blit_scaled extension.

V2: Use integer array instead of a string.
    Bump up the comment.

V3: Use uint8_t type array.

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
1 file changed