Rename ARCH_RMOBILE_BOARD_STRING to ARCH_RENESAS_BOARD_STRING
because all the chips are made by Renesas, while only a subset
of them is from the R-Mobile line.

Use the following command to perform the rename:

"
$ git grep -l 'ARCH_RMOBILE_BOARD_STRING' | \
  xargs -I {} sed -i 's@ARCH_RMOBILE_BOARD_STRING@ARCH_RENESAS_BOARD_STRING@g' {}
"

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Paul Barker <paul.barker.ct@bp.renesas.com>