Improve USB gaming keyboard support.

Add support for decoding pressed keys as a bitmap. The keys in the
bitmap are described in the interface specific HID descriptor. Some
keyboards even have multiple input interfaces, only using the bitmap
method when the event array is full. That typically means when more
than seven keys are pressed simultaneously.

The internals of the USB keyboard driver have been slightly reworked
to keep track of all keys in a single bitmap having 256 bits. This
bitmap is then divided into blocks of 64-bits as an optimisation.

Simplify automatic key repeat logic, because only the last key pressed
can be repeated.

PR: 224592
PR: 233884
Tested by: Alex V. Petrov <alexvpetrov@gmail.com>
MFC after: 1 week
Sponsored by: Mellanox Technologies