RISCV: dts: jh7110-starifive-visionfive-2: Add a gpio-restart node

RISCV: dts: jh7110-starifive-visionfive-2: Add a  gpio-restart node

Add a gpio-restart node to do reset.
Before applied this patch, System Reset Extension doesn't appear with
sbi command.

OpenSBI 1.3
Machine:
  Vendor ID 489
  Architecture ID 8000000000000007
  Implementation ID 4210427
Extensions:
  sbi_set_timer
  sbi_console_putchar
...[snip]...
  IPI Extension
  RFENCE Extension
  Hart State Management Extension
  Performance Monitoring Unit Extension

After applied this patch, System Reset Extension is supported from SBI.

OpenSBI 1.3
Machine:
  Vendor ID 489
  Architecture ID 8000000000000007
  Implementation ID 4210427
Extensions:
  sbi_set_timer
  sbi_console_putchar
...[snip]...
  IPI Extension
  RFENCE Extension
  Hart State Management Extension
  System Reset Extension
  Performance Monitoring Unit Extension

Change-Id: Idf298b22ff2fb728ddade59befa741718e9c2466
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>