kernel: init: introduce a new init level: ARCH

We have cases where some devices needs to be initialized very early and
before c_start is call, i.e. to setup very early console or to setup
memory. Traditionally this would be hardcoded as part of the soc layer
and not using device model or the init levels.

This patch adds a new level ARCH, which will be called in early
architecture code and before we jump to the kernel code.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>