drm/vmwgfx: Fix SET_SHADER_CONST emulation on guest-backed devices

Emulate the SET_SHADER_CONST legacy command on guest-backed devices by
issuing a SET_GB_SHADERCONSTS_INLINE command.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>