arm: dts: k3: Add support for packaging sysfw.itb and tiboot3.bin

arm: dts: k3: Add support for packaging sysfw.itb and tiboot3.bin

Board config binary artifacts must be generated to be used by binman to
package sysfw.itb and tiboot3.bin for all K3 devices.

For devices that follow combined flow, these board configuration
binaries must again be packaged into a combined board configuration
blobs to be used by binman to package tiboot3.bin.

Add common k3-binman.dtsi to generate all the board configuration
binaries needed.

Also add custMpk.pem and ti-degenerate-key.pem needed for signing GP and
HS bootloader images common to all K3 devices.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Neha Malcom Francis <n-francis@ti.com>