drm/xe/uapi: Separate VM_BIND's operation and flag

Use different members in the drm_xe_vm_bind_op for op and for flags as
it is done in other structures.

Type is left to u32 to leave enough room for future operations and flags.

v2: Remove the XE_VM_BIND_* flags shift (Rodrigo Vivi)

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/303


Signed-off-by: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>