kernel-devicetree: install dtb files without -${KERNEL_DTB_NAME} suffix

* we were installing them with -${KERNEL_DTB_NAME} suffix
  and then adding a symlink without this suffix if
  KERNEL_IMAGETYPE_SYMLINK is set:
  if [ "${KERNEL_IMAGETYPE_SYMLINK}" = "1" ] ; then
    ln -sf $dtb_base_name-${KERNEL_DTB_NAME}.$dtb_ext $deployDir/$dtb_base_name.$dtb_ext
  fi

  and another one when KERNEL_DTB_LINK_NAME is set:
  if [ -n "${KERNEL_DTB_LINK_NAME}" ] ; then
    ln -sf $dtb_base_name-${KERNEL_DTB_NAME}.$dtb_ext $deployDir/$dtb_base_name-${KERNEL_DTB_LINK_NAME}.$dtb_ext
  fi

  but KERNEL_DEVICETREE variable doesn't include this
  -${KERNEL_DTB_NAME} suffix, so everything which uses KERNEL_DEVICETREE
  either needs to add it as well or depend on KERNEL_IMAGETYPE_SYMLINK
  being set, e.g. IMAGE_BOOT_FILES variable used by do_image_wic is
  generated by make_dtb_boot_files function here:
  https://github.com/agherzan/meta-raspberrypi/blob/2ad4dd667affb72bdbbc2d6b5f7b50589f506b31/conf/machine/include/rpi-base.inc#L118


  and do_image_wic fails without KERNEL_IMAGETYPE_SYMLINK:
  | WARNING: bootloader config not specified, using defaults
  |
  | ERROR: _exec_cmd: install -m 0644 -D deploy/images/raspberrypi4-64/bcm2711-rpi-4-b.dtb image/1.0-r1/tmp-wic/boot.1/bcm2711-rpi-4-b.dtb returned '1' instead of 0
  | output: install: cannot stat 'deploy/images/raspberrypi4-64/bcm2711-rpi-4-b.dtb': No such file or directory

  we can fix the function to append -${KERNEL_DTB_NAME} or we can
  change this to install without suffix and then add ${KERNEL_DTB_NAME}
  link only when KERNEL_DTB_NAME is set (${MACHINE} by default)

* now it looks strange to have both KERNEL_DTB_LINK_NAME and KERNEL_DTB_NAME
  symlinks, but keep it for backwards compatibility and it will make
  more sense again together with the rest of [YOCTO #12937] where version
  specific *_LINK_NAME links are created as hardlinks in separate do_deploy_links
  task.

[YOCTO #12937]

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>