drm/amd/display: Replace inline NUM_ELEMENTS macro with ARRAY_SIZE

drm/amd/display: Replace inline NUM_ELEMENTS macro with ARRAY_SIZE

Replaces the use of local NUM_ELEMENTS macro with the ARRAY_SIZE macro
defined in <linux/array_size.h>.

This aligns with existing coccinelle script array_size.cocci which has
been applied to other sources in order to remove inline
sizeof(a)/sizeof(a[0]) patterns from other source files.

Suggested-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Linus Probert <linus.probert@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>