drm/amdgpu: save the reset dump register value for devcoredump

Allocate memory for register value and use the same values for devcoredump.
v1 -> v2: Change krealloc_array() to kmalloc_array()
v2 -> v3: Fix alignment

Signed-off-by: Somalapuram Amaranath <Amaranath.Somalapuram@amd.com>
Reviewed-by: Shashank Sharma <Shashank.sharma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>