input: misc: hbtp_input compile drm callbacks properly

Compile DRM callbacks inside compilation flag, so that
it should register for the same only if DRM feature is
enabled in defconfig.
DRM callbacks are used for SDM845 and SDM670 target only.
Other targets like SDM450, SDM632 and SDM439 don't use this.

Change-Id: Ifcee2f3a0af474cd674decef7739a447ee120bf4
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>