drm: fixed: Add dfixed_frac

This helper macro retrieves the fractional part of a fixed20_12 20.12
fixed-point number.

Signed-off-by: Robert Morell <rmorell@nvidia.com>
Signed-off-by: Olof Johansson <olofj@chromium.org>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/drm_fixed.h

@@ -37,6 +37,7 @@ typedef union dfixed {
 #define dfixed_init(A) { .full = dfixed_const((A)) }
 #define dfixed_init_half(A) { .full = dfixed_const_half((A)) }
 #define dfixed_trunc(A) ((A).full >> 12)
+#define dfixed_frac(A) ((A).full & ((1 << 12) - 1))
 
 static inline u32 dfixed_floor(fixed20_12 A)
 {