[armhf] enable SERIAL_8250_OMAP and SERIAL_8250_OMAP_TTYO_FIXUP

The UART on am335x has two drivers: omap_uart and a variant of the 8250 driver omap8250. In commit ca8be8fc2c30 ("ARM: dts: am33xx-l4: fix UART compatible") that is included in v6.18-rc1 the am335x device tree was changed that only the omap8250 driver can be used going forward. Up to now only the omap_uart was enabled. So to have a driver for that device, enable the omap8250.

One issue while switching is that the two drivers use different base names for the serial devices (ttyO* for omap_uart and ttyS* for omap8250). To soften the transition also enable SERIAL_8250_OMAP_TTYO_FIXUP which automatically falls back to ttySx if console=ttyOx was given on the command line.