lib: utils/timer: Allow ACLINT MTIMER supporting only 32-bit MMIO

We can have ACLINT MTIMER devices which only support 32-bit MMIO
accesses on RV64 system so this patch adds a boolean DT property
"mtimer,no-64bit-mmio" to detect this from MTIMER DT node.

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