arm64: zynqmp: Move SoC sources to mach-zynqmp

Similar changes was done for Zynq in past and this patch just follow
this pattern to separate cpu code from SoC code.

Move arch/arm/cpu/armv8/zynqmp/* -> arch/arm/mach-zynqmp/*
And also fix references to these files.

Based on
"ARM: zynq: move SoC sources to mach-zynq"
(sha1: 0107f240)

Signed-off-by: Michal Simek <michal.simek@xilinx.com>