drm/amdgpu: simplify amdgpu_ras_eeprom.c

All chips that support RAS also support IP discovery, so
use the IP versions rather than a mix of IP versions and
asic types.  Checking the validity of the atom_ctx pointer
is not required as the vbios is already fetched at this
point.

v2: add comments to id asic types based on feedback from Luben

Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Luben Tuikov <luben.tuikov@amd.com>