drm: amd/acp: fix broken menu structure

Fix the Kconfig dependencies so that the menu is presented
correctly by adding a dependency on DRM_AMDGPU to the "menu"
Kconfig statement.  This makes a continuous dependency on
DRM_AMDGPU in the DRM AMD menus and eliminates a broken menu
structure.

Fixes: a8fe58ce ("drm/amd: add ACP driver support")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: David (ChunMing) Zhou <David1.Zhou@amd.com>
Cc: Maruthi Bayyavarapu <maruthi.bayyavarapu@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>