ARM: Remove unused PARAMS_PHYS from arch/arm/boot/compressed

The only reference in arch/arm/boot/compressed to PARAMS_PHYS is
params() in head.S, which can be directly converted to the exact
address as specified by arch/arm/mach-rpc/Makefile.boot.

Signed-off-by: Eric Miao <eric.miao@canonical.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>