drm/amd/display: Rename should_use_dmub_lock to reflect inbox1 usage

drm/amd/display: Rename should_use_dmub_lock to reflect inbox1 usage

[Why]
Newer DCN use the DMCUB HW lock via inbox0 for performance reasons while
older ones will use inbox1.

The should_use_dmub_lock() function does not describe whether the lock
in general should be used, but whether it should be used via inbox1.

[How]
Rename the function to should_use_dmub_inbox1_lock() to reflect this.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>