drm: fix nouveau_acpi build

Fix build errors when CONFIG_ACPI is enabled but MXM_WMI is not enabled
by selecting both MXM_WMI and ACPI_WMI (the latter just for kconfig
dependencies):

nouveau_acpi.c:(.text+0x2400c8): undefined reference to `mxm_wmi_call_mxmx'
nouveau_acpi.c:(.text+0x2400cf): undefined reference to `mxm_wmi_call_mxds'
nouveau_acpi.c:(.text+0x2400fe): undefined reference to `mxm_wmi_call_mxmx'
nouveau_acpi.c:(.text+0x2402ba): undefined reference to `mxm_wmi_supported

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>