binman: bintool: Change make target arg type from string to list

The argument type of `build_from_git` was changed from string to list
in d71e7116997f14097735f04cc7847f0a68dbc485.

This commit adapts the argument type of all bintools using this
function.

Signed-off-by: Lukas Funke <lukas.funke@weidmueller.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>

binman: btool: Add Xilinx Bootgen btool

Add the Xilinx Bootgen as bintool. Xilinx Bootgen is used to create
bootable SPL (FSBL in Xilinx terms) images for Zynq/ZynqMP devices. The
btool creates a signed version of the SPL. Additionally to signing the
key source for the decryption engine can be passend to the boot image.

Signed-off-by: Lukas Funke <lukas.funke@weidmueller.com>

binman: btool: Add Xilinx Bootgen btool

Add the Xilinx Bootgen as bintool. Xilinx Bootgen is used to create
bootable SPL (FSBL in Xilinx terms) images for Zynq/ZynqMP devices. The
btool creates a signed version of the SPL. Additionally to signing the
key source for the decryption engine can be passend to the boot image.

Signed-off-by: Lukas Funke <lukas.funke@weidmueller.com>