fix #28506983

Some ARM machines may have large memory capacity (e.g., more than 256G),
or large hole(s) in memory layout among nodes.

Kernel with CONFIG_ARM64_VA_BITS as 39 has the linear region size as
256G, and the memory that we will not be able to cover with the linear
mapping shall be removed. This may cause part of the physical memory to
become unavailable, system deadlock on memory, or even boot failure, on
such ARM machines.

This changes CONFIG_ARM64_VA_BITS to 48 which supports 128T linear
mapping, in order to adapt to most scenarios.
Signed-off-by: NXu Yu <xuyu@linux.alibaba.com>
Reviewed-by: NShile Zhang <shile.zhang@linux.alibaba.com>
Reviewed-by: NCaspar Zhang <caspar@linux.alibaba.com>