Support stepping through PPC PLT with securePLT.

Support stepping through PPC PLT with securePLT.

	* configure.tgt (powerpc-*-linux*): Add glibc-tdep.o.
	* ppc-linux-tdep.c: Include glibc-tdep.h.
	(powerpc32_plt_stub, powerpc32_plt_stub_so): Add PLT stub templates.
	(powerpc_linux_in_plt_stub): New function.
	(powerpc_linux_in_dynsym_resolve_code): New function.
	(ppc_skip_trampoline_code): New function.
	(ppc_linux_init_abi): Use PPC specific functions rather than generic.
	Use glibc_skip_solib_resolver.