uboot: mark Freescale i.MX28 specific formats as such

It's rather unclear that uboot.sb, uboot.sd and uboot.nand are
Freescale i.MX28 specific, so let's make that clear in the prompt of
each option, like we do for the Marvell-specific uboot.kwb.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

boot/uboot/Config.in

@@ -178,11 +178,11 @@ config BR2_TARGET_UBOOT_FORMAT_ELF
 
 config BR2_TARGET_UBOOT_FORMAT_SB
 	depends on BR2_arm
-	bool "u-boot.sb"
+	bool "u-boot.sb (Freescale i.MX28)"
 
 config BR2_TARGET_UBOOT_FORMAT_SD
 	depends on BR2_arm
-	bool "u-boot.sd"
+	bool "u-boot.sd (Freescale i.MX28)"
 	help
 	  This is Freescale i.MX28 SB format, with a header for booting
 	  from an SD card.
@@ -194,7 +194,7 @@ config BR2_TARGET_UBOOT_FORMAT_SD
 
 config BR2_TARGET_UBOOT_FORMAT_NAND
 	depends on BR2_arm
-	bool "u-boot.nand"
+	bool "u-boot.nand (Freescale i.MX28)"
 	help
 	  This is Freescale i.MX28 BootStream format (.sb), with a header
 	  for booting from a NAND flash.