drivers: dma_mcux_lpc: Add Kconfig to reduce data

Add a Kconfig to have the ability to fine tune the amount of RAM that
the driver uses based on the number of channels expected to be used.

Most of the code is already there but just need this Kconfig to get the
benefit of it by reducing the size of the statically created arrays.

Also change the number of channels field in the configuration to a byte
instead of a 32 bit integer because that should be sufficient to
describe the number of DMA channels.

Rename LPC DMA Driver Kconfigs with namespace to MCUX_LPC

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>