ARM: dts: aspeed: Grow u-boot partition 64MiB OpenBMC flash layout

ARM: dts: aspeed: Grow u-boot partition 64MiB OpenBMC flash layout

Aspeed AST2600 u-boot requires 600KiB+ flash space. Sharing the same
openbmc-flash-layout-64.dtsi requires to resize the flash partition.

The updated flash layout as follows:
- u-boot: 896 KiB
- u-boot-env: 128 KiB
- kernel: 9MiB
- rofs: 32 MiB
- rwfs: 22 MiB

Signed-off-by: Troy Lee <troy_lee@aspeedtech.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20210316085932.2601-1-troy_lee@aspeedtech.com
Signed-off-by: Joel Stanley <joel@jms.id.au>