aarch64,vcpu: Add CNTKCTL_EL1 register to vcpu_t

This register is accessible from EL1 and affects whether Generic Timer
registers are accessible from EL0. When switching out of guests, the
kernel needs to restore the correct access for native threads.

Signed-off-by: Kent McLeod <Kent.Mcleod@data61.csiro.au>

Convert license tags to SPDX identifiers

This commit also converts our own copyright headers to directly use
SPDX, but leaves all other copyright header intact, only adding the
SPDX ident. As far as possible this commit also merges multiple
Data61 copyright statements/headers into one for consistency.

arm-hyp: check vtimer irq state before masking

Without an invariant, during verification we no longer know that the
virtual timer irq is not inactive in restore_virt_timer, necessitating
an extra check.

arm-hyp: provide MODIFIES info for DONT_TRANSLATE

C parser cascades up DONT_TRANSLATE blocking modifies proofs, unless
some kind of spec is provided. This makes the claim that the timer
register getters don't modify any global state, and the setters modify
only state verification does not care about.

arm_hyp: Save and restore vtimer state on switches

Added support for reading and writing additional virtual timer
registers for vcpu hw read and write accesses. These include the
compare value register (CNTV_CVAL) and offset register (CNTV_OFF),
each represented as two 32 bit (high and low) registers on aarch32 and
as single 64 bit registers on aarch64.

Added support for explicitly saving and restoring the virtual
timer registers when the vcpu is enabled and disabled. This
ensures when the vcpu is switched in and out, the virtual timer
registers are restored to a state that is consistent to when
it was last run.

By default the CNTVOFF register will be updated by the kernel to
accumulate the time the VCPU is not running. From the guest this will
result in the VCNT register not increasing when the VCPU is suspended.
This behavior can be turned off by disabling the
KernelArmVtimerUpdateVOffset config option.

arm: tickless generic timer implementation

Update the generic timer to implement the MCS kernels tickless timer
driver API and update all platforms that use the arm generic timers:

- bcm2837
- exynos5
- hikey
- imx7
- odroidc2
- tk1
- tx1
- tx2
- zynq7000

Also move the generic timer constants to machine.h to avoid a circular
dependency.

arm: remove plat/machine/timer.h

plat/machine/timer.h is unused on arm, so remove it and fix up the
includes.

arm: generic_timer -> drivers/timer/arm_generic

- move generic_timer.h to drivers/timer/arm_generic.h
- update all configs that use it.

timer-refactor: Move kernel timers and rename

This change moves all arm platform timers to drivers/timer
and renames them to the compatibility string specified in the dts.
Now the correct timer is included at build time based on the dts,
this follows the same pattern as the serial-refactor.
Have moved the arm generic_timer and priv_timer into the timer
folder and updated cmake configs appropriately.