MIPS: Purple: Fix multiple definition error on final linking of u-boot binary

The linker of recent toolchains complains about multiple definitions
on final linking of u-boot binary. This patch removes all redundant
object files from u-boot.lds those are already added to .text section
by the linker.

That patch could not be tested but the resulting u-boot.map still looks
good. The start symbol is at 0xB0000000, the environment at 0xB0008000
so u-boot should boot.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@googlemail.com>
Cc: Wolfgang Denk <wd@denx.de>
Signed-off-by: Shinya Kuribayashi <skuribay@pobox.com>