tgsi: add simple tgsi_is_msaa_target() helper
tgsi: add simple tgsi_is_msaa_target() helper

Reviewed-by: Jose Fonseca <61b5a29db2c0650f7c8510f93eece059c1b09320@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler