drm/amd/ras: bound CPER record fetch buffer size

drm/amd/ras: bound CPER record fetch buffer size

Bound CPER record fetch allocation by buffer size.

v2: Drop redundant cap on cper_num and raise
    GET_CPER_RECORD max buffer size.

Suggested-by: YiPeng Chai <YiPeng.Chai@amd.com>
Signed-off-by: Candice Li <candice.li@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>