Inline resetTimer for all platforms

- for arm generic timer platforms, we remove resetTimer ->
resetGenericTimer indirection and simply include generic_timer.h
- this reduces boiler plate for platforms that share timer drivers, as
they simply include the one header
- there is far more timer code in the RT kernel, which motivates this
change

Make TIMER_CLOCK_HZ available in timer.h for ARM

The RT kernel needs this value accessible to common functions.

Trivial: remove excess whitespace

Refactor arm timer ticks calculations

- remove a lot of redundancy
- define TIMER_CLOCK_HZ for each platform (rather than inconsistenly
named variables with inconsist units)
- use the common calculation of TIMER_RELOAD

Refactor memory mapped arm timers

- make them consistent: struct, type and global vars
- typedef the struct definition as volatile
- separate struct, typedef and variable definition
- always cast the pointer as the timer type

Remove many DONT_TRANSLATE markers.

The vast majority of the DONT_TRANSLATE markers in the kernel are used
to hide __asm__ statements and builtin functions
(e.g. __builtin_unreachable ()) from the C-to-Isabelle parser.

The parser now supports underscore identifiers and many __asm__ statements,
and the builtin functions are prototyped, meaning the vast majority of the
DONT_TRANSLATE markers can be dropped. The remaining markers cover functions
that must be treated specially.

Release snapshot