[PATCH] arm64: restore info->page_offset and implement paddr_to_vaddr_arm64()

commit 94c97db3 (arm64: Get 'info->page_offset' from PT_LOAD segments
to support KASLR boot cases) added a method to determine info->page_offset
(PAGE_OFFSET) from PT_LOAD segments for arm64 platforms to support
--mem-usage option, but its hardcoded condition did not work correctly
on several systems.

This patch restores the method to determine PAGE_OFFSET value, which
is same as kernel's definition, and determine info->phys_offset from
PT_LOAD by using PAGE_OFFSET. With these two values, implement
paddr_to_vaddr_arm64() to support --mem-usage option.

Tested-by: Bhupesh Sharma <bhsharma@redhat.com>
Signed-off-by: Kazuhito Hagio <k-hagio@ab.jp.nec.com>