cmake: linker: arm: put RAM sections in RAM region

Cleanup RAM layout so that the RAM_REGION is now in the RAM memory
region.  Put .bss in RAM_REGION.

This means we have a proper program header for the RAM region.

As part of this extend zephyr_linker_symbol to allow it to take
an OBJECT paramater to specify the region to associate a symbol to.

Signed-off-by: Kumar Gala <kumar.gala@intel.com>