Input: synaptics-rmi4 - clean up F30 implementation

This patch does several cleanup changes to F30 code

- switch to using BIT() macro
- use DIV_ROUND_UP() where appropriate
- factor out code setting up and reporting buttons
- use single loop when reporting buttons: arithmetic is cheap compared to
  conditionals and associated branch misprediction.
Tested-By: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>