blk: Hide the BLK and SPL_LEGACY_BLOCK options

We don't want boards to be able to change these. They can be handled
as dependencies of options that need them, such as SPL_MMC. There is no
point in enabling the block interface without any storage devices to
create a block device.

Hide both options from the 'menuconfig' display and deny their use in
defconfig files.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index e82a779..707e2bc 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -1,5 +1,5 @@
 config BLK
-	bool "Support block devices"
+	bool # "Support block devices"
 	depends on DM
 	default y if MMC || USB || SCSI || NVME || IDE || AHCI || SATA
 	default y if EFI_MEDIA || VIRTIO_BLK || PVBLOCK
@@ -12,7 +12,7 @@
 	  A filesystem can be placed in each partition.
 
 config SPL_LEGACY_BLOCK
-	bool "Enable Legacy Block Device"
+	bool # "Enable Legacy Block Device"
 	depends on SPL && !DM_SPL
 	default y if SPL_MMC || SPL_USB_STORAGE || SCSI || NVME || IDE
 	default y if SPL_AHCI_PCI