[GDBserver] Use pre-generated amd64-linux tdesc as test
    
    Now, all these amd64-linux pre-generated tdesc can be used as test, so
    don't need to build them if $development is false.
    
    Note that this patch wants to remove ipa_x32_linux_regobj, but it was
    removed by mistake by 22049425ce40324139be82d9a6ec518c46b65815.
    
    gdb/gdbserver:
    
    2017-06-09  Yao Qi  <yao.qi@linaro.org>
    
    	* configure.srv: Empty srv_amd64_linux_regobj if $development is
    	false.
    	(ipa_amd64_linux_regobj): Remove.