arm: dts: k3-j784s4-binman.dtsi: Clean up and templatize boot binaries

arm: dts: k3-j784s4-binman.dtsi: Clean up and templatize boot binaries

Clean up templatized boot binaries for j784s4 soc. This includes
modifying the k3-j784s4-binman.dtsi to use SPL_BOARD_DTB,
BOARD_DESCRIPTION and UBOOT_BOARD_DESCRIPTION from the files that
include it to further reuse code.

k3-j784s4-binman.dtsi will contain only templates. Only required boot
binaries can be built from the templates in the boards' respective
-u-boot.dtsi file (or k3-<board>-binman.dtsi if it exists). This allows
clear distinction between the SoC common stuff vs. what is additionally
needed to boot up a specific board.

Signed-off-by: Neha Malcom Francis <n-francis@ti.com>
[ Do it only for j784s4 ]
Signed-off-by: Manorit Chawdhry <m-chawdhry@ti.com>