drm/amdgpu: Rename aqua_vanjaram_reg_init.c

This contains SOC specific functions, rename to a more generic format
<soc>.c => aqua_vanjaram.c

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>