trivial: style changed

sel4bench: add SEL4BENCH_RESET_CCNT for arm

This is not possible on x86, but required on arm if a benchmark is
relying on the 32bit cycle count not overflowing.

libsel4bench: use ccnt_t as appropriate

libsel4bench: armv8 aarch64 support

- add PMU_READ and PMU_WRITE macros for accessing the PMU
- refactor aarch32/armv8 constants into mode specific directory, use PMU_READ
and PMU_WRITE in functions that access the PMU
- add constants for aarch64/armv8

Fix licenses

Use CONFIG_ variables instead of configuration definitions

sel4bench: reset all counters

Resetting a subset of the counters a) doesn't work on all platforms c)
doesn't make much sense and b) is less code, d) unused functionality

If this functionality is required it can be readded in a working form at
a later date.

sel4bench: use 'mask' instead of 'counters'

This avoids confusion in loops that used to modify both 'counter' and
'counters'

sel4bench: style

sel4bench: use ccnt_t and remove duplicate

Was duplicated sel4bench_counter_t and format function

sel4bench: improve interface

- define array of generic events
- drop generic events that don't exist for all platforms (i.e are not
generic)
- define number of generic events
- define types to illustate the difference between a counter and an
event

sel4bench: remove layer of indirection in events

No longer required now directory structure is fixed.

sel4bench: use #pragma once

sel4bench: fix include structure and licenses

For too long sel4bench has relied on relative includes
and filenames with the CPU/ARMV in it.

Finally fix it.

libsel4bench: Correct armv8 license headers

Include armv8 support for PMU event numbers