drivers: counter: Add AGT counter driver support for Renesas RA8

- boards: renesas: Add support for agt.
- drivers: counter: Add support for counter driver use agt
- dts: arm: Add support for agt.
- dts: bindings: Add support for agt counter driver.
- soc: renesas: Add support for agt counter driver.
- samples: drivers: counter: alarm: Add support for RA8

This is initial support with only basic functionality for counter
operation on Zephyr using AGT hardware, current support for
count source is limited to LOCO and PCLKB, other count source
like underflow signal external pin or AGTIO from another AGT
channel will be added in later support

Signed-off-by: Ha Nguyen <ha.nguyen.fz@bp.renesas.com>
Signed-off-by: Thao Luong <thao.luong.uw@renesas.com>
Signed-off-by: Duy Phuong Hoang. Nguyen <duy.nguyen.xa@renesas.com>
Signed-off-by: Khoa Nguyen <khoa.nguyen.xh@renesas.com>