ui/spice: Create another texture with linear layout when gl=on is enabled

Since most encoders (invoked by Spice) may not work with tiled memory
associated with a texture, we need to create another texture that has
linear memory layout and use that instead.

Note that, there does not seem to be a direct way to indicate to the
GL implementation that a texture's backing memory needs to be linear.
Instead, we have to do it in a roundabout way where we need to first
create a tiled texture and import that as a memory object to create
a new texture that has a linear memory layout.

Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>