drm/amd/display: use swap() helper macro in bios_parser

Use swap() helper macro instead of open coded swap instructions. The
change also facilitates code cleanup and realignment for improved
readability.  Issue identified using swap.cocci Coccinelle semantic
patch script.

Signed-off-by: Deepak R Varma <drv@mailo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>