ARM: mvebu: Makefile clean-up

Some objects depend on CONFIG_ARCH_MVEBU whereas this whole Makefile
depends on the same symbol. Moreover CONFIG_ARCH_MVEBU can't be
selected as a module. So we can simplify this Makefile by moving all
the object from obj-$(CONFIG_ARCH_MVEBU) to obj-y.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>