[ARM] arm64: Fix defterm early mapping in initial MMU LPAE setup

The initial MMU LPAE setup uses "&defterm_early_base" to determine
virtual address of defterm early mapping.

On ARM64, "&x" gives us absolute address of variable "x" based on
current execution address and not compile time address of "x".

This means that on arm64 "&defterm_early_base" will give absolute
virtual address based on current load address because the function
_setup_initial_ttbl() is called with MMU disabled from load address.

Due to all this, defterm early base in initial MMU LPAE setup is
mapped to wrong location.

This patch fixes use of "&defterm_early_base" in _setup_initial_ttbl().

Signed-off-by: Anup Patel <anup@brainfault.org>