imx: mx7: move get_boot_device to cpu.c

Move get_boot_device to cpu.c to prepare adding i.MX8M support,
because i.MX8M share same code with i.MX7.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Stefano Babic <sbabic@denx.de>
diff --git a/arch/arm/include/asm/mach-imx/boot_mode.h b/arch/arm/include/asm/mach-imx/boot_mode.h
index e3ed046..300868a 100644
--- a/arch/arm/include/asm/mach-imx/boot_mode.h
+++ b/arch/arm/include/asm/mach-imx/boot_mode.h
@@ -31,6 +31,15 @@
 	BOOT_DEV_NUM = UNKNOWN_BOOT,
 };
 
+/* Boot device type */
+#define BOOT_TYPE_SD		0x1
+#define BOOT_TYPE_MMC		0x2
+#define BOOT_TYPE_NAND		0x3
+#define BOOT_TYPE_QSPI		0x4
+#define BOOT_TYPE_WEIM		0x5
+#define BOOT_TYPE_SPINOR	0x6
+#define BOOT_TYPE_USB		0xF
+
 struct boot_mode {
 	const char *name;
 	unsigned cfg_val;