drm/amdgpu/display: Use u64 divide macro for round up division

[why]
Fix compilation warnings on i386 architecture:
undefined reference to `__udivdi3'
[how]
Switch DIV_ROUND_UP to DIV64_U64_ROUND_UP

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>