mesa: use _mesa_check_sample_count() for multisample textures

mesa: use _mesa_check_sample_count() for multisample textures

Extends _mesa_check_sample_count() to properly support the
TEXTURE_2D_MULTISAMPLE and TEXTURE_2D_MULTISAMPLE_ARRAY targets, which
have subtly different limits than renderbuffers.

This resolves the remaining TODO in the implementation of
TexImage*DMultisample.

V2: - Don't introduce spurious block.
    - Do this in multisample.c instead.
    - Fix typo in error message.
    - Inline spec quotes

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>