MIPS: remove CONFIG_MIPS_LD_CAN_LINK_VDSO

Given commit e4412739 ("Documentation: raise minimum supported
version of binutils to 2.25"), CONFIG_MIPS_LD_CAN_LINK_VDSO is always
'y'.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>