[U-Boot] [RFC] Merge all ns16550 dm serial drivers into one

Hi,

Currently there are 5 dm serial drivers, all of which are ns16550 compatible drivers. They are:

serial_omap.c serial_dw.c serial_tegra.c serial_x86.c serial_ppc.c

All these drivers are pretty much similar. I think we can justmerge these into one ns16550 driver.

If you think this is necessary, I will send a patch series to do this.

Regards, Bin