Merged in david_s5/nuttx-1/david_s5/kconfig-edited-online-with-bitbucket-1463078993637 (pull request #19)

Kconfig edited online with Bitbucket

sam_xdmac.c edited online with Bitbucket

sam_xdmac.c edited online with Bitbucket

Since I can't (yet) get rid of the sanity checks in config.h, I suppose I should at least update the checks.

Backout d5be40be.  This change is logically correct but unmasks a lot of issues.  Reverted for now.

tools/mkconfig.c:  Go further... remove all autogenerated sanity checks from the config.h header file

Remove CONFIG_FS_READABLE/WRITABLE logic from tools/mkconfig.c.  This logic has been replaced with proper logic in the Kconfig files, it is out of date and an ongoing maintenance problem, and it shoulw not be necessary.

Allows the use of tmpfs when no block driver is available. This is correctly done to define NONBDFS but below the structure is not where it should be.