arm64: Fix the soft_restart routine

Change the soft_restart() routine to call cpu_reset() at its identity mapped
physical address.

The cpu_reset() routine must be called at its identity mapped physical address
so that when the MMU is turned off the instruction pointer will be at the correct
location in physical memory.

Signed-off-by: Geoff Levand <geoff@infradead.org> for Huawei, Linaro
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>