MIPS: qemu-mips: use the unified u-boot.lds script

Remove the board specific linker script. It is not
needed anymore, the unified MIPS linker script can
be used instead.

All qemu_mips targets are producing identical binary
images after the change than before.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: Daniel Schwierzeck <daniel.schwierzeck@googlemail.com>