serial: 8250_platform: Enable generic 16550A platform devices

serial: 8250_platform: Enable generic 16550A platform devices

Currently, 8250_platform driver is used only for devices with fixed
serial ports (plat_serial8250_port). Extend this driver for any generic
16550A platform devices which can be probed using standard hardware
discovery mechanisms like ACPI.

This is required in particular for RISC-V which has non-PNP generic
16550A compatible UART that needs to be enumerated as ACPI platform
device.

Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Link: https://lore.kernel.org/r/20240730051218.767580-1-sunilvl@ventanamicro.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>