[Why&How]
When using a 4k monitor when cursor caching is not supported due to
framebuffer being on an uncacheable address, enabling display refresh
from MALL would trigger corruption if SS is enabled.

Prevent entering SS if we are on the edge case and cursor caching is not
possible. Do this only if cursor size larger than a 64x64@4bpp. Pull the
cursor size calculation out of if condition since cursor address may not
be set on all platforms
Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Brian Chang <Brian.Chang@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>