drm/amd/display: fix i386 frame size warning

Addresses the following warning:
drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn30/display_mode_vba_30.c:3596:6: error: stack frame size (2092) exceeds limit (2048) in 'dml30_ModeSupportAndSystemConfigurationFull' [-Werror,-Wframe-larger-than]
void dml30_ModeSupportAndSystemConfigurationFull(struct display_mode_lib *mode_lib)
     ^

UseMinimumDCFCLK() is eating away at
dml30_ModeSupportAndSystemConfigurationFull()'s stack space, so use a
pointer to struct vba_vars_st instead of passing lots of large arrays
as parameters by value.

Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>