arch/arm: Enable caching

Signed-off-by: Pawel Dziepak <pdziepak@quarnos.org>
arch/arm: Add SP804 timer driver

 * Add atomic operations for ARM
 * Add system time measurement on raspberry pi
 * Add basic IRQ controller support for raspberry pi

Signed-off-by: Pawel Dziepak <pdziepak@quarnos.org>