Which these changes DMA now works on the LPC54xx

Squashed commit of the following:

    arch/arm/src/lpc54xx:  SDMMC fixes.. DMA should not be enabled on non-DMA transfers, the burst setting in FIFOTH is supposed to match the burst setting in the BMOD reseters, Add DMA error interrupt support.
    arch/arm/src/lpc54xx:  Mostly costmetic changes to the SDMMC driver.