svga: new SVGA_MSAA env var to disable/enable MSAA pixel formats
svga: new SVGA_MSAA env var to disable/enable MSAA pixel formats

On by default.

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

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler