drm: vkms: Adds XRGB_16161616 and ARGB_1616161616 formats

This will be useful to write tests that depends on these formats.

ARGB and XRGB follows the a similar implementation of the former formats.
Just adjusting for 16 bits per channel.

V3: Adapt the handlers to the new format introduced in patch 7 V3.
V5: Minor improvements
    Added le16_to_cpu/cpu_to_le16 to the 16 bits color read/writes.

Reviewed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Igor Torrente <igormtorrente@gmail.com>
Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220905190811.25024-9-igormtorrente@gmail.com