drm/amdgpu: fw_attestation: fix unused function warning

Without debugfs, the compiler notices one function that is not used at
all:

drivers/gpu/drm/amd/amdgpu/amdgpu_fw_attestation.c:123:12: error: unused function 'amdgpu_is_fw_attestation_supported' [-Werror,-Wunused-function]

In fact the static const amdgpu_fw_attestation_debugfs_ops structure is
also unused here, but that warning is currently disabled.

Removing the #ifdef check does the right thing and leads to all of this
code to be dropped without warning.

Fixes: 19ae3330

 ("drm/amdgpu: added support for psp fw attestation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>