svga: add a separate function to get dx format capabilities from vgpu10 device

svga: add a separate function to get dx format capabilities from vgpu10 device

Currently we have one function to get format capabailities and
we convert DX10 devcaps back to DX9. This can be confusing.
Going forward we will have a separate function for dealing with dx formats.

This patch also fixes the depth stencil devcap. Instead of hardcoding
the capabilities for the depth stencil formats, we will inquire the
device for the capabilities. Note: we will still need to explicity set
the SVGA3D_DXFMT_SHADER_SAMPLE bit for SVGA3D_R32_FLOAT_X8X24 and
SVGA3D_R24_UNORM_X8 since this bit is not advertised but supported
by the 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>