drm/amd/display: include soc._clock_tmp[] into DC's scratch region

Currently, we are using soc._clock_tmp[] to temporarily store and modify
data from soc.clock_limits[] before copying it back into
soc.clock_limits[] (because modifying data directly in
soc.clock_limits[] causes unintended behavior). However, this approach
has a number of downsides, such as:

	1. struct _vcs_dpi_soc_bounding_box_st's creation/destruction
	   aren't well defined (which could mean more unintended
	   behavior).
	2. Throwing "temp" varibles in structs everywhere doesn't make
	   for a particularly readable codebase.

For these reasons, we should get rid of soc._clock_tmp[] by defining a
struct scratch within struct dc that, contains within it all of the
temporary variables (including _clock_tmp[]) such that it is obvious how
they are intended to be used.

Co-authored-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>