SAMA5 does not build when executing from SDRAM before board frequencies are not constant.  Rather, the bootloader configures the clocking and we must derive the clocking from the MCK left by the bootloader.  This means lots more computations.  This is untested on initial commit because I don't have a good PWM test setup right now.

GPDMA driver for the LPC43xx.  The GPDMA block is basically the same as the LPC17xx.  Only the clock configuration is different and LPC43xx has four different DMA request sources, where LPC17xx has only two.

boardctl:  Add new command to start the NX server as a kernel thread.  Also refresh more configurations.

NX:  Remove configuration CONFIG_NX_NXSTART.  nx_start.c is now built unconditionally in multi-user mode.