svga: assign a separate function for is_format_supported() for vgpu10 device

svga: assign a separate function for is_format_supported() for vgpu10 device

This patch adds a new function svga_is_dx_format_supported() to check
for format support in a VGPU10 device.

v2: reapply the patch after svga_is_format_supported is moved to svga_format.c

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Neha Bhende <bhenden@vmware.com>