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

NFS: Fix prototype of unbind method.  The function prototype was not updated for NFS after a recent change to the file system interface.  From Manuel Stühn.

In ARMV71-Xplained clock configuration, divider was set to 25 to get 25*12MHz=300MHz CPU clock.  The correct multiplier is 24 becaue the calculatin if (24+1)*12MHz.  So the board was running at 312MHz.  From Efim Monjak.

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.