glamor: Add glamor_copy_fbo_cpu() for CopyArea to non-GPU destination

This provides a speedup e.g. when the destination is an SHM pixmap.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76285


Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Keith Packard <keithp@keithp.com>