ARM: mvebu: rename armada-370-xp.c to board-v7.c

In preparation to the introduction of the support of Armada 375 and
Armada 38x, this commit renames arch/arm/mach-mvebu/armada-370-xp.c to
arch/arm/mach-mvebu/board-v7.c. The board-v7.c name as we expect this
file to ultimately contain the DT_MACHINE_START definitions for all
ARMv7 Marvell EBU platforms (370, 375, 38x, XP and Dove as of today).

In relation to this file rename, this commit also:

 * Renames the hidden Kconfig symbol MACH_ARMADA_370_XP to
   MACH_MVEBU_V7. This hidden symbol is selected by the various
   per-SoC visible Kconfig options to trigger the build of board-v7.c.

 * Renames a certain number of functions in board-v7.c so that their
   armada_370_xp prefix is replaced by a mvebu prefix. The .dt_compat
   array keeps its armada_370_xp prefix because the new SOCs will be
   introduced with separate .dt_compat arrays, due to the need for
   different SMP operations.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>