drm/msm: Remove DRM_MSM_NUM_IOCTLS

The ioctl array is sparsely populated but the compiler will make sure
that it is sufficiently sized for all the values that we have so we
can safely use ARRAY_SIZE() instead of having a constantly changing
#define in the uapi header.

Change-Id: Ic0dedbad39f30abb8ce340289089d2f3a5f6fe36
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>