drivers/*/Kconfig: Consolidate driver Kconfig Files.

This commit does two things:

1. First, it reorganizes the driver Kconfig files so that each is self contained.  Before, a part of the driver configuration was in drivers/Kconfig and the rest was in in drivers/xyz/Konfig.  Now, all of the driver configuration is consolitated in the latter.

2. Second, this commit correct numerous serious errors introduced in a previous reorganization of the driver Kconfig files.  This was first noted by Nicholas Chin in PR270 for the case of the drivers/i2c/Kconfig but some examination indicates that the error was introduced into several other Kconfig files as well.

The nature of the introduced error was basically this:

- Nothing must intervene between the menuconfig selection and the following conditional configuration otpions.
- A previous PR erroneously introduced unconditional options between the menuconfig and the following confditional logic, thus corrupting the driver menus.

This error was easy to make because the driver Kconfig files were not well modularized.  Making them fully self-contained should eliminate this kind of error in the future.

drivers/mtd/Kconfig

@@ -3,9 +3,20 @@
 # see the file kconfig-language.txt in the NuttX tools repository.
 #
 
-if MTD
+menuconfig MTD
+	bool "Memory Technology Device (MTD) Support"
+	default n
+	---help---
+		Memory Technology Device (MTD) drivers.  Some simple drivers for
+		memory technologies like FLASH, EEPROM, NVRAM, etc.  See
+		include/nuttx/mtd/mtd.h
 
-comment "MTD Configuration"
+		(Note: This is a simple memory interface and should not be
+		confused with the "real" MTD developed at infradead.org.  This
+		logic is unrelated; I just used the name MTD because I am not
+		aware of any other common way to refer to this class of devices).
+
+if MTD
 
 config MTD_PARTITION
 	bool "Support MTD partitions"