ARM: zynq: Remove all unused mach headers

Remove empty unused mach/hardware.h.
mach/irqs.h is unused because SPARSE_IRQ are ON by default.
mach/timex.h is unused because of CONFIG_ARCH_MULTIPLATFORM.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Tested-by: Josh Cartwright <josh.cartwright@ni.com>