arm: aarch32: Use proper sys functions for cache mainteinance

This patchset is fixing two things:

1. The proper sys_* functions are used for cache mainteinance
   operations.

2. To check the status of the L1 cache the SCB registers are probed so
   the code is assuming a core architecture cache is present, thus make
   the code conditionally compiled on CONFIG_ARCH_CACHE.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>