xtensa: move #include <linker/common-*.ld> up

Move linker/common-rom.ld between .rodata sections so that it's together
with other immutable data.
Move linker/common-ram.ld before the .bss section, so that .bss does not
appear between data sections, which had two consequences:
- there's a .bss-sized gap in the ELF image, and
- PHDR segment that covers .bss overlaps the segment that covers .data,
  resulting in the following xt-run warning:

  ( [ sample_controller ] load_bfd ) *WARNING* Executable segment
    [ 60004d60, 600079a7 ] overlaps an existing executable segment

Change-Id: I2db46f4656e240016fe60883057cc000b6377180
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>