drm/msm: Fix build with KMS disabled

When commit 98290b0a ("drm/msm: make it possible to disable
KMS-related code.") was rebased on top of commit 3bebfd53 ("drm/msm:
Defer VMA unmap for fb unpins"), the additional use of msm_kms was
overlooked, resulting in a build break when KMS is disabled.  Add some
additional ifdef to fix that.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 98290b0a ("drm/msm: make it possible to disable KMS-related code.")
Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>
Tested-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Jessica Zhang <jessica.zhang@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/663240/