firmware: port built-in section to linker table

This ports built-in firmware to use linker tables,
this replaces the custom section solution with a
generic solution.

This also demos the use of the .rodata (SECTION_RO)
linker tables.

Tested with 0 built-in firmware, 1 and 2 built-in
firmwares successfully.

v3: explicitly include tables.h as we no longer
    include tables.h from sections.h

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>