arm: mvebu: configs: helios4: Change U-Boot offset on SPI Flash

arm: mvebu: configs: helios4: Change U-Boot offset on SPI Flash

SPI flash support on Helios4 [1] has been merge to u-boot/master on
commit 8cb8c0c6a83bef ("Merge git://git.denx.de/u-boot-marvell")

However, the SPI image build failed after the merge with following
message:

COPY    spl/u-boot-spl.bin
MKIMAGE u-boot-spl.kwb
Error: Image header (incl. SPL image) too big!
header=0x20816 CONFIG_SYS_U_BOOT_OFFS=0x20000!
Increase CONFIG_SYS_U_BOOT_OFFS!
Error: Image header (incl. SPL image) too big!
header=0x20816 CONFIG_SYS_U_BOOT_OFFS=0x20000!
Increase CONFIG_SYS_U_BOOT_OFFS!
Could not create image
Makefile:1162: recipe for target 'u-boot-spl.kwb' failed
make: *** [u-boot-spl.kwb] Error 1

Let's increase the u-boot offset to 0x30000 to accommodate SPL changes
and leave some margin for future changes.

[1] https://patchwork.ozlabs.org/patch/1007762/

Signed-off-by: Aditya Prayoga <aditya@kobol.io>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Stefan Roese <sr@denx.de>