firmware-utils: mktplinkfw: rework combined image option

firmware-utils: mktplinkfw: rework combined image option

We use combined option in "mktplinkfw" tool for generating initramfs
kernel images and header for kernel inside "safeloader" image type (in
fact, only for TL-WR1043ND v4 at this moment).

There is also "mktplinkfw-kernel" tool, a stripped-down version, used
only for generating "simple" header, for safeloader image types.

This changes how "mktplinkfw" handles combined images (which then will
allow us to drop the stripped-down version of the tool):

- drop "ignore size" command line option (it was used only for combined
  images anyway)
- don't require "flash layout id" for combined images (we don't need and
  shouldn't limit size of the initramfs kernel and for kernels inside
  safeloader images, the "tplink-safeloader" tool does the size check)
- require kernel address and entry point in command line parameters for
  combined images (consequence of previous point)
- don't include md5 sum and firmware length values in header (they are
  needed only for update from vendor GUI and are ingored in case of
  initramfs and "tplink-safeloader" images)
- drop "fake" flash layout for TL-WR1043ND v4 as it's no longer needed

Also, adjust "mktplinkfw-combined" command in ar71xx/image/tp-link.mk to
match introduced changes in "mktplinkfw" tool.

Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>