drm/amdgpu: add ras_eeprom_read_idx interface

drm/amdgpu: add ras_eeprom_read_idx interface

PMFW will manage RAS eeprom data by itself, add new interface to read
eeprom data via PMFW, we can read part of records by setting index.

v2: use IPID parse interface.
    pa is not used and set it to a fixed value.
v3: optimize the null pointer check for IPID parse interface.

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>