tests/amdgpu: add missing config.h include

Otherwise we'll end up without the macros set during configure stage.
And effectively error out in sanity tests such as the mmap static
assert.

To reproduce, do a multilib build - 32bit build on 64bit machine.

Cc: Fabio Pedretti <pedretti.fabio@gmail.com>
Cc: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Fixes: 33dcc29f ("amdgpu: Add VMID reservation per GPU context test.")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104819


Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>