xtensa: intel_adsp: align SoC initialization with SOF

This aligns the SoC initialization with the one in SOF,
especially the manipulation of clock control and power control
registers. These registers are not entirely the same across
CAVS versions, so we need to deal with them according to
which version we are building for. This also consolidates
the macros for these registers to the one provided by SOF
(soc/shim.h) to avoid duplication. Another note is that
the usage of clock gating bit was not correct. In SOF,
clock gating of SoC cores should be allowed but the old code
in Zephyr prevented clock gating, which has the potential to
prevent the whole DSP from going into low power mode.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>