lib: utils: Support CLINT with 32bit MMIO access on RV64 system

It is possible to have a CLINT implementation which supports
only 32bit MMIO accesses on RV64 system so this patch extends
our CLINT driver such that platform code can specify whether
CLINT supports 64bit MMIO access.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish <Patra&lt;atish.patra@wdc.com>
Reviewed-by: Zong Li <zong.li@sifive.com>