DRV2605L Continuous Haptic Feedback Support (#6461)

DRV2605L Continuous Haptic Feedback Support (#6461)

* provide means to turn on RTP mode and set the amplitude

* new keycode HPT_CONT to turn RTP off/on

* introduce new keycodes HPT_CONI, and HPT_COND for Haptic Continuous Increase and Decrease

* support for continuous mode amplitude increase and decrease

* code cleanup

* update docs to reference new keycodes and functionality

* don't touch the keymaps

* add function prototypes

* add proper guards

* cleanup guards

* remove extra reserved