rockchip: rk3588-rock-5b: Update defconfig

Update defconfig for rk3588-rock-5b with new defaults.

Remove the SPL_ROCKCHIP_BACK_TO_BROM=y option, SPL is expected to load
next stage from a FIT image and then jump to next stage not back to
BootRom.

Extend SPL_MAX_SIZE to 0x40000, SPL is loaded to 0x0 and TF-A is loaded
to 0x40000, use the space in between as SPL_MAX_SIZE.

Add config option to include useful gpio cmd.

Remove the CONFIG_NET_RANDOM_ETHADDR=y option, ethaddr and eth1addr is
set based on cpuid read from OTP.

Add CONFIG_SYS_NS16550_MEM32=y to use 32bit access of serial register.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>