kernel: Activate CONFIG_ARM64_SW_TTBR0_PAN

This activates the CONFIG_ARM64_SW_TTBR0_PAN option for all arm64
kernels by default.

The CONFIG_ARM64_SW_TTBR0_PAN option prevents the kernel form accessing
user space memory directly. This makes it harder to exploit the kernel.

This is activated by default and was already activate on all other arm64
targets before.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>