touchscreen: Fix errors due to assumption of CONFIG_FB always being set

oplus_touchscreen's touchpanel_common.h's touchpanel_data struct
contains the `fb_notif` field only if CONFIG_FB is set. However, that
field gets used to register as notifier clients for both fb and msm_drm.
Fix this by letting this field appear if either CONFIG_FB or
CONFIG_MSM_DRM is set instead.

oplus_touchscreen's touchpanel_common_driver.c's fb_notifier_callback()
would cast the incoming data pointer to a `struct fb_event *`,
regardless of whether this callback was registered for fb or msm_drm.
Fix this by having it cast to a `struct msm_drm_notifier*` instead if
CONFIG_DRM_MSM is defined.

All the oplus touchscreen drivers populated their dev_pm_ops structs
with suspend/resume functions only if CONFIG_FB is set. Fix this by
having the preprocessor check for CONFIG_FB or CONFIG_DRM_MSM instead.

synaptics_dsx's synaptics_dsx_rmi_dev.c calls send_sig_info(), but if
CONFIG_FB isn't set, then the implicit linux/sched/signal.h include gets
lost. Explicitly include linux/sched/signal.h to fix this.

Change-Id: Ibe00a070b57eac78f3492603d73b4869d099a9d9