Use dts support from U-Boot via OF_SEPARATE instead of depending from opensbi.

This would help to make the necessary changes in drivers and device trees
in U-Boot tree itself. This feature would also be helpful to not pass
dtb during opensbi builds.
Signed-off-by: NJagan Teki <jagan@amarulasolutions.com>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>
Reviewed-by: NAnup Patel <anup.patel@wdc.com>
Signed-off-by: NRick Chen <rick@andestech.com>

configs/sifive_fu540_defconfig

@@ -7,8 +7,9 @@ CONFIG_RISCV_SMODE=y
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_FIT=y
 CONFIG_MISC_INIT_R=y
+CONFIG_DEFAULT_DEVICE_TREE="hifive-unleashed-a00"
 CONFIG_DISPLAY_CPUINFO=y
 CONFIG_DISPLAY_BOARDINFO=y
-CONFIG_OF_PRIOR_STAGE=y
+CONFIG_OF_SEPARATE=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_DM_MTD=y

doc/board/sifive/fu540.rst

@@ -58,10 +58,7 @@ firmware. We need to compile OpenSBI with below command:
 
 .. code-block:: none
 
-    make PLATFORM=sifive/fu540 FW_PAYLOAD_PATH=<path to u-boot.bin> FW_PAYLOAD_FDT_PATH=<path to hifive-unleashed-a00.dtb from Linux>
-
-(Note: Prefer hifive-unleashed-a00.dtb from Linux-5.3 or higher)
-(Note: Linux-5.2 is also fine but it does not have ethernet DT node)
+make PLATFORM=sifive/fu540 FW_PAYLOAD_PATH=<path to u-boot-dtb.bin>
 
 More detailed description of steps required to build FW_PAYLOAD firmware
 is beyond the scope of this document. Please refer OpenSBI documenation.