linux-imx

powerpc: Fix build on some non-freescale platforms

Commit 9deaa53ac7fa373623123aa4f18828dd62292b1a broke build
on platforms that use legacy_serial.c without also having
CONFIG_SERIAL_8250_FSL enabled due to an unconditional code
to a routine in that module.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>