ARM: arm1176: Define arch_cpu_init() at the SoC level

Commit 86c63265 "ARM: arm1176: enable instruction cache in
arch_cpu_init()" defined arch_cpu_init() in a file that is shared across
all arm1176 SoCs. tnetv107x already implemented this function, which
caused linking to break. Move the new conflicting arch_cpu_init() into
arm1176/bcm2835/init.c so that it doesn't conflict; grep indicates this
function is usually defined at the SoC-level, not the CPU-level, at least
for ARM.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
Acked-by: Marek Vasut <marex@denx.de>