timer: starfive: Add Starfive timer support

Add timer driver in Starfive SoC. It is an timer that outside
of CPU core and inside Starfive SoC.

Signed-off-by: Kuan Lim Lee <kuanlim.lee@starfivetech.com>
Signed-off-by: Wei Liang Lim <weiliang.lim@starfivetech.com>

Changes for v2:
- correct driver name, comment, variable
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>