mesa: don't enable GL_EXT_framebuffer_multisample for software drivers

Note: This is a candidate for the 9.0 branch.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
(cherry picked from commit 8f3c81d0182b10d99976dd0a80f10eebebf54017)

Conflicts:

	src/mesa/main/extensions.c
1 file changed