The arch_timer driver supports a superset of the functionality of the
arm_generic driver, and is not tied to a particular arch.

This patch moves arm64 to use the arch_timer driver, gaining additional
functionality in doing so, and removes the (now unused) arm_generic
driver. Timer-related hooks specific to arm64 are moved into
arch/arm64/kernel/time.c.
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Acked-by: NMarc Zyngier <marc.zyngier@arm.com>
Acked-by: NSantosh Shilimkar <santosh.shilimkar@ti.com>