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.

rockpro64, bcm2837, qemu-arm-virt: specify NUM_PPI

This is needed to enable succesful compilation with SMP on.
Even though the bcm2837 doesn't (yet) support SMP, add the value
for completeness.

cmake: add helper functions

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.

CMake: Invert plat config.cmake processing order

Instead of processing each platform CMake file during the arch's
config.cmake file, we process all of the platform CMake files first.
This is primarily motivated by wanting to move platform configuration
into a config file that is processed via a -C argument to the initial
build initialisation command.

Now a platform config is responsible for setting the kernel architecture
and it's own platform/arch specific config settings. Where previously a
platform was chosen in an arch specific way via either setting
KernelARMPlatform or KernelX86Sel4Arch or KernelRiscVPlatform, a
platform can now be set by KernelPlatform. In cases where a platform may
further parameterise its configuration it is free to choose its own
config options to query. Platforms that support multiple seL4
architectures should use KernelSel4Arch to query this. Platforms that
provide sub platforms such as exynos5 and subplatforms exynos5250,
exynos5410 and exynos5422 can be selected by specifying
KernelPlatform=exynos5, KernelARMPlatform=exynos5410 for example.

CMake: KernelHaveFPU is valid for all aarch64

Instead of setting this option on each platform that supports aarch64,
we set it for all aarch64 platforms. It is expected that every valid
aarch64 platform has an FPU and will be correctly context switched by
the kernel.

arm: generic_timer -> drivers/timer/arm_generic

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

bcm2837: use declare_default_headers

- remove unused header files replaced by declare_default_headers
- move machine.h to drivers/irq/bcm2836-armctrl-ic.h

style: use consistent styling for all cmake files

Add .cmake-format.yaml which defines custom functions with kwargs to
style nicely

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.

serial-refactor: Refactor kernel serial drivers

Have added a drivers/serial folder to kernel, where all serial drivers
will be kept. The point is to have the the dts parsed and generate cmake
to include the right uart.c file prefixed with the compatibility.
Have removed all io.c from plat and includes from plat/config.cmake and
updated CHANGES file.

arm: Remove empty level2 cache code

Arm generic timer: Remove wrapper functions

exynos5 platforms have to initialise custom hardware before initialising
the generic timer. This was forcing every other platform to call a
wrapper function. We instead define initTimer that exynos5 can override.

arm: use DTS to generate memory region lists

This changes all ARM platforms over to using the device tree found in
the kernel to generate memory region information.

rpi3/aarch64: add cmake targets for aarch64

Move arm generic timer initTimer to c file

This prepares to inline the resetTimer definition from generic_timer.h
without creating a mess of circular includes

Add a CMake based build system

This commit adds an alternate build system using CMake that operates indepenently of
the existing Kconfig+Kbuild+make based build system