board: starfive: spl: Support jtag for VisionFive2 board

JTAG pins are mapped as below. To access the JTAG pins, we need to
control the GPIO pins from SPL which seems to be the earliest stage for
JTAG.

- JTAG nTRST:	GPIO36 / Input
- JTAG TDI:	GPIO61 / Input
- JTAG TMS:	GPIO63 / Input
- JTAG TCK:	GPIO60 / Input
- JTAG TDO:	GPIO44 / Output

Signed-off-by: Chanho Park <chanho61.park@samsung.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>