virgl: Fake MSAA when max samples is 1

virgl: Fake MSAA when max samples is 1

When the host is running on softpipe/llvmpipe the maximum number of
samples for multisampling is 1. GL 3.0 requires at least 4 samples, and
softpipe/llvmpipe get around this by enabling PIPE_CAP_FAKE_SW_MSAA.

This patch mimics softpipe/llvmpipe behavior in virgl by enabling the
same PIPE_CAP_FAKE_SW_MSAA workaround when the max sample count reported
by the host is 1. This change allows virgl on a softpipe/llvmpipe host
to advertise support for GL 3.0 and beyond.

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>
Reviewed-By: Gert Wollny <gert.wollny@collabora.com>