lib: sbi: Print timer frequency at boot time

We now have frequency in timer device instance provided by platform
so let's print timer frequency as part of the boot prints.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Xiang W <wxjstz@126.com>