drm/amd/display: Remove use of division operator for long longs

In fixed31_32.h, in dc_fixpt_shl,'/' was used for division of one long
long int by another long long int.  As there is no inbuilt long long
int division function in c, gcc inserted its own.  However, gcc does not
link the library that contains this function.  To avoid this, use
bitwise operators instead of /

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>