ARM: P2V: avoid initializers and assembly using PHYS_OFFSET

As PHYS_OFFSET will be becoming a variable, we can't have it used in
initializers nor assembly code.  Replace those in generic code with
a run-time initialization.  Replace those in platform code using the
individual platform specific PLAT_PHYS_OFFSET.

Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Acked-by: David Brown <davidb@codeaurora.org>
Acked-by: Eric Miao <eric.y.miao@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>