arm64: defconfig: Enable LPA2 support

arm64: defconfig: Enable LPA2 support

We typically enable support in defconfig for all architectural features
for which we can detect at runtime if the hardware actually supports
them.

Now that we have implemented support for LPA2 based 52-bit virtual
addressing in a way that should not impact 48-bit operation on non-LPA2
CPU, we can do the same, and enable 52-bit virtual addressing by
default.

Catalin adds:

  Currently the "Virtual address space size" arch/arm64/Kconfig menu
  entry sets different defaults for each page size. However, all are
  overridden by the defconfig to 48 bits. Set the new default in
  Kconfig and remove the defconfig line.

[ardb: squash follow-up fix from Catalin]

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240214122845.2033971-86-ardb+git@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>