drm/amdgpu: convert bios_hardcoded_edid to drm_edid

Instead of manually passing around 'struct edid *' and its size,
use 'struct drm_edid', which encapsulates a validated combination of
both.

As the drm_edid_ can handle NULL gracefully, the explicit checks can be
dropped.

Also save a few characters by transforming '&array[0]' to the equivalent
'array' and using 'max_t(int, ...)' instead of manual casts.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>