gallium/winsys/kms: Fully initialize kms_sw_dt at prime import time (v2)

gallium/winsys/kms: Fully initialize kms_sw_dt at prime import time (v2)

Currently kms_sw_displaytarget_add_from_prime() allocates the struct and
fills in only some of the fields, resulting in a half-baked struct that
needs to be further completed by the caller. To make this a bit more
consistent, pass width, height and stride to this function and fill in
everything there, so that caller can take the returned struct as is.

v2: Split from one big patch into four fixing one thing at a time.

Signed-off-by: Tomasz Figa <tfiga@chromium.org>
CC: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>