libplatsupport: omap3 ltimer refactor

This refactors the omap3 ltimer to use the new
driver framework APIs.
- IRQ Chip parser "copied" off avic.c
- Change array-based ABS and REL timer distinction
into two different variables
- gpt_create() sets up mappings, while
abs_gpt_init()/rel_gpt_init() set up the registers
- Change some signatures to void
- IRQ handler moved to timer driver
- IRQ handler logic is shared between 'abs' and
'rel' timers, behaviour differs on how they were
initialised

Fixes for omap ltimer

- always use the rel gpt for timeouts as the logic is too complex and
error prone for abs_gpt. Stick to using abs_gpt to measure the time.
- handle relative and absolute timeouts > the max for the gpt.

libplatsupport: Initialize prescaler value

Failing to initialize the prescaler value in the `gpt` struct has two affects
* The passed in configuration value for the prescaler is ignored, violating the interface
* The `prescaler` value in the gpt struct is an arbitrary uninitialized value resulting
in garbage usages of the prescaler value

libplatsupport: Calculate prescaler ticks correctly

The comments on the PTV register (which controls prescaling) state that the timer
is prescaled by 2^(PTV+1), not by PTV+1. This commit simply makes the code reflect
the stated arithmetic.

libplatsupport: Preserve omap timer configuration when stopping

Completely clearing the tclr register throws away any configured prescaler (and other)
settings, resulting in a timer that does not match the cached configuration leading to
garbage timing. As `gpt_start` only enables the `ST` bit and does not perform a full
`gpt_init` `gpt_stop` should therefore only disable the `ST` bit

trivial: fix whitespace

Implement ltimer for omap

- remove pstimer support
- combine absolute_gpt and relative_gpt, gpt.h into one file

fix licenses

Remove trailing whitespace

libplatsupport: Add absolute timer driver for omap

libplatsupport: Add absolute timer driver for omap