ns9xxx: prepare for adding support for Digi ns921x processors

The hardware team changed some things that were taken as being common to
all ns9xxx processors up to now.

This patch addresses:

- irqs: s/IRQ_/IRQ_NS9360_/

- system module registers: some registers are still general, their
  definition lives now in include/asm-arm/arch-ns9xxx/regs-sys-common.h.
  The ns9360 specific ones are in .../regs-sys-ns9360.h
  As a result ns9360_systemclock cannot be static inline any more as its
  definition needs regs-sys-ns9360.h.  This becomes a real problem when
  adding support for ns9215 as this will need regs-sys-ns9215.h and
  including both files will not work.  For the same reason
  ns9360_reset() is now non-inline and gpio functions live in their own
  file.

- register mapping: s/ns9xxx_map_io/ns9360_map_io/

- timer registers:  move time.c to time-ns9360.c;
  s/ns9xxx_timer/ns9360_timer/

Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>