fs/iso9660: use 'depends on' instead of 'select' for bootloader

In preparation to the introduction of the support for other
bootloaders than Grub, this commit switches from having the iso9660
support "select" the necessary bootloader to using a "depends on".

The main motivation is that the isolinux bootloader support will
really need to do a "depends on", due to the need of having a certain
option enabled, but this option being a kconfig "choice".

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

fs/iso9660/Config.in

@@ -2,6 +2,7 @@ config BR2_TARGET_ROOTFS_ISO9660
 	bool "iso image"
 	depends on (BR2_i386 || BR2_x86_64)
 	depends on BR2_LINUX_KERNEL
+	depends on BR2_TARGET_GRUB
 	select BR2_LINUX_KERNEL_INSTALL_TARGET \
 	       if (!BR2_TARGET_ROOTFS_ISO9660_INITRD && !BR2_TARGET_ROOTFS_INITRAMFS)
 	help
@@ -25,7 +26,7 @@ choice
 
 config BR2_TARGET_ROOTFS_ISO9660_GRUB
 	bool "grub"
-	select BR2_TARGET_GRUB
+	depends on BR2_TARGET_GRUB
 	select BR2_TARGET_GRUB_FS_ISO9660
 
 endchoice
@@ -52,6 +53,6 @@ config BR2_TARGET_ROOTFS_ISO9660_INITRD
 
 endif
 
-comment "iso image needs a Linux kernel to be built"
+comment "iso image needs a Linux kernel and grub to be built"
 	depends on BR2_i386 || BR2_x86_64
-	depends on !BR2_LINUX_KERNEL
+	depends on !BR2_LINUX_KERNEL || !BR2_TARGET_GRUB