rockchip: rk3308: Implement checkboard() to print SoC variant

Implement checkboard() to print current SoC variant used by a board,
e.g. one of:

  SoC:   RK3308
  SoC:   RK3308B
  SoC:   RK3308B-S

when U-Boot proper is running.

  U-Boot 2025.01-rc1 (Nov 02 2024 - 20:26:25 +0000)

  Model: Radxa ROCK Pi S
  SoC:   RK3308B
  DRAM:  512 MiB (effective 510 MiB)

Information about the SoC variant is read from GRF.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>

arch/arm/mach-rockchip/rk3308/rk3308.c

@@ -216,3 +216,19 @@ int arch_cpu_init(void)
 	return 0;
 }
 #endif
+
+#define RK3308_GRF_CHIP_ID	0xFF000800
+
+int checkboard(void)
+{
+	u32 chip_id = readl(RK3308_GRF_CHIP_ID);
+
+	if (chip_id == 0x3308)
+		printf("SoC:   RK3308B\n");
+	else if (chip_id == 0x3308c)
+		printf("SoC:   RK3308B-S\n");
+	else
+		printf("SoC:   RK3308\n");
+
+	return 0;
+}