Revert "gallium: Force blend color to 16-byte alignment"

Revert "gallium: Force blend color to 16-byte alignment"

This reverts commit d8d6091a846ac2a40a011d512d6d57f6c8442e6a.

Heap allocations may be only 8-byte aligned on 32-bit system, and so having
members with 16-byte alignment (such as in the case where pipe_blend_color is
embedded in radeonsi's si_context) is undefined behavior which indeed causes
crashes when compiled with gcc -O3.

Cc: <mesa-stable@lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96835
Signed-off-by: Tim Rowley <timothy.o.rowley@intel.com>
Acked-by: Chuck Atkins <chuck.atkins@kitware.com>