drm/amdgpu/display: provide ASSERT macros unconditionally

It seems impossible to build this driver without setting either
CONFIG_DEBUG_KERNEL or CONFIG_DEBUG_DRIVER:

drivers/gpu/drm/amd/amdgpu/../display/dc/dm_services.h: In function 'set_reg_field_value_ex':
drivers/gpu/drm/amd/amdgpu/../display/dc/dm_services.h:132:2: error: implicit declaration of function 'ASSERT'; did you mean 'IS_ERR'? [-Werror=implicit-function-declaration]

This moves the ASSERT() macro and related helpers outside of
the #ifdef to get it to build again.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>