svga: Avoid bouncing buffer data in malloced buffers

svga: Avoid bouncing buffer data in malloced buffers

Some constant- and texture upload buffer data may bounce in malloced
buffers before being transferred to hardware buffers. In the case of
texture upload buffers this seems to be an oversight. In the case of
constant buffers, code comments indicate that we want to avoid mapping
hardware buffers for reading when copying out of buffers that need
modification before being passed to hardware. In this case we avoid
data bouncing for upload manager buffers but make sure buffers that
we read out from stay in malloced memory.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>