[AArch64] Implement gdbarch_core_read_description
    
    Recommit with missing header files added.
    
    gdb/
    	* aarch64-linux-tdep.c: Include "auxv.h" and "elf/common.h".
    	(aarch64_linux_core_read_description): New function.
    	(aarch64_linux_init_abi): Register gdbarch_core_read_description.