MIPS: Netlogic: Remove XLR early serial setup

The early serial code is not needed because we already have early
printk support provided by common/earlycons.c

This change also fixes the following build error that occurs when
CONFIG_SERIAL_8250 is not configured for Netlogic XLR boards:

arch/mips/built-in.o: In function `nlm_early_serial_setup':
setup.c:(.init.text+0x274): undefined reference to `early_serial_setup'
make: *** [vmlinux] Error 1

Reported-by: Markos Chandras <markos.chandras@imgtec.com>
Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/6083/