K3: Add ATF_K3_USART_OFFSET setting

Add ATF_K3_USART_OFFSET flag while building ATF as needed for SK-AM68
platform.

Signed-off-by: Beleswar Padhi <b-padhi@ti.com>

Author: 3V3RYONE

config/sources/families/k3.conf

@@ -34,7 +34,7 @@ case "${BRANCH}" in
 esac
 
 ATF_PLAT="k3"
-ATF_TARGET_MAP="PLAT=$ATF_PLAT TARGET_BOARD=$ATF_BOARD DEBUG=1 bl31;;build/$ATF_PLAT/$ATF_BOARD/debug/bl31.bin:bl31.bin"
+ATF_TARGET_MAP="PLAT=$ATF_PLAT TARGET_BOARD=$ATF_BOARD DEBUG=1 ${ATF_K3_USART_OFFSET} bl31;;build/$ATF_PLAT/$ATF_BOARD/debug/bl31.bin:bl31.bin"
 
 UBOOT_TARGET_MAP="BL31=bl31.bin TEE=bl31.bin BINMAN_INDIRS=${SRC}/cache/sources/ti-linux-firmware all;;tiboot3.bin ${SYSFW_FILE:+sysfw.itb} tispl.bin u-boot.img"