platform: generic: Add Sifive FU540 TLB flush range limit override

We need to override the remote TLB flush range limit for SiFive FU540
so we add platform override to achieve this.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>