drm/amdgpu: Add PSP public function to load a list of FWs

v1: Adds a function to load a list of FWs as passed by the caller. This is
needed as only a select need to loaded for some use cases.

v2: Omit unrelated change, remove info log, fix return value when count is 0

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