rockchip: px30: list possible SPL boot devices

BOOTROM sets a bit in a CPU register so that the software can know from
where the first stage bootloader was booted. One use case for this is to
specify the default loading medium for U-Boot proper to match the one
used by the BOOTROM to load the SPL (same-as-spl in
u-boot,spl-boot-order).

Let's create the mapping between BOOTROM value and Device Tree node
names for MMC devices.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>

arch/arm/mach-rockchip/px30/px30.c

@@ -8,6 +8,7 @@
 #include <init.h>
 #include <asm/armv8/mmu.h>
 #include <asm/io.h>
+#include <asm/arch-rockchip/bootrom.h>
 #include <asm/arch-rockchip/grf_px30.h>
 #include <asm/arch-rockchip/hardware.h>
 #include <asm/arch-rockchip/uart.h>
@@ -15,6 +16,11 @@
 #include <asm/arch-rockchip/cru_px30.h>
 #include <dt-bindings/clock/px30-cru.h>
 
+const char * const boot_devices[BROM_LAST_BOOTSOURCE + 1] = {
+	[BROM_BOOTSOURCE_EMMC] = "/mmc@ff390000",
+	[BROM_BOOTSOURCE_SD] = "/mmc@ff370000",
+};
+
 static struct mm_region px30_mem_map[] = {
 	{
 		.virt = 0x0UL,