Fix a Cortex-A compilation error in the vfork() logic when system calls are enabled in modes other than CONFIG_BUILD_KERNEL.

arch/arm/src/sama5/sam_ehci.c:  Fix some bad conditional compilation that left a function undefined if CONFIG_USBHOST_ASYNCH is not selected.

Fix references to the no-longer-existent misc/ directory in comments, README files, and documentation

Back out another error introduced with commit 02c33f66c5a8be774034cd40e4125e9323c7b4d8. Causes an infinite loop in up_lowputc().

Remove conditional logic form non-SAM4CM parts (Gregory Nutt)

Back out an error introduced with commit 02c33f66c5a8be774034cd40e4125e9323c7b4d8.  Causes an infinite loop in up_lowputc().  From Max Neklyudov.

SAML21 DMA: Fix a logic error.  Since the write back descriptors overly the base descriptors, we need to do some special things in order to correctly free any allocated descriptors