Comment # 3 on bug 1073193 from Andreas F�rber

Thanks, I'll bump SERIAL_8250_NR_UARTS to 32 for all applicable architectures,
including i386 pae, for consistency.

Not knowing this driver too well, I'm doing a test build for whether we can
lower SERIAL_8250_RUNTIME_UARTS to 0 on Arm platforms while at it.