drm/amdgpu: Remove the redundant code of psp bootloader functions

The psp bootloader functions code of psp_v13_0.c had been
optimized before. According the code style of psp_v13_0.c
to remove the redundant code of psp_v11_0.c.

v2: squash in drop unused variable (Alex)

Signed-off-by: yipechai <YiPeng.Chai@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>