mkimage: Add support for bundling TEE in mkimage -f auto

mkimage: Add support for bundling TEE in mkimage -f auto

Introduce two new parameters to be used with mkimage -f auto to bundle
TEE image into fitImage, using auto-generated fitImage. Add -z to specify
TEE file name and -Z to specify TEE load and entry point address. This is
meant to be used with systems which boot all of TEE, Linux and its DT from
a single fitImage, all booted by U-Boot.

Example invocation:
"
$ mkimage -E -A arm -C none -e 0xc0008000 -a 0xc0008000 -f auto \
          -d arch/arm/boot/zImage \
          -b arch/arm/boot/dts/st/stm32mp135f-dhcor-dhsbc.dtb \
          -z ../optee_os/out/arm-plat-stm32mp1/core/tee-raw.bin \
	  -Z 0xde000000 \
          /path/to/output/fitImage
"

Documentation update and test are also included, the test validates
both positive and negative test cases, where fitImage does not include
TEE and does include TEE blobs.

Acked-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Marek Vasut <marek.vasut@mailbox.org>