Currently, the start address of physical memory is obtained by masking
the program counter with a fixed mask of 0xf8000000.  This mask value
was chosen as a balance between the requirements of different platforms.
However, this does require that the start address of physical memory is
a multiple of 128 MiB, precluding booting Linux on platforms where this
requirement is not fulfilled.

Fix this limitation by validating the masked address against the memory
information in the passed DTB.  Only use the start address
from DTB when masking would yield an out-of-range address, prefer the
traditional method in all other cases.  Note that this applies only to the
explicitly passed DTB on modern systems, and not to a DTB appended to
the kernel, or to ATAGS.  The appended DTB may need to be augmented by
information from ATAGS, which may need to rely on knowledge of the start
address of physical memory itself.

This allows to boot Linux on r7s9210/rza2mevb using the 64 MiB of SDRAM
on the RZA2MEVB sub board, which is located at 0x0C000000 (CS3 space),
i.e. not at a multiple of 128 MiB.
Suggested-by: Nicolas Pitre <nico@fluxnic.net>
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>