riscv: remove dram_init_banksize()

riscv: remove dram_init_banksize()

Remove dram_init_banksize() on the architecture level.

Limiting used RAM to under 4 GiB is only necessary for CPUs which have a
DMA issue. SoC specific code already exists for FU540, FU740, JH7110.

Not all RISC-V boards will have memory below 4 GiB.

A weak implementation of dram_init_banksize() exists in common/board_f.c.

See the discussion in
https://lore.kernel.org/u-boot/545fe813-cb1e-469c-a131-0025c77aeaa2@canonical.com/T/

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Anup Patel <anup@brainfault.org>