PowerPC VLE sh_flags and p_flags

PowerPC VLE sh_flags and p_flags

ELF section sh_flags SHF_PPC_VLE was being set based on arch/mach,
which meant all code sections in an object file has the flag or all
lacked it.  We can do better than that.  Only those code sections
where VLE is enabled ought to have the flag, allowing an object file
to contain both VLE and non-VLE code.

Also, ELF header p_flags PF_PPC_VLE wasn't being set, and segments
were being split unnecessarily.

bfd/
	* elf32-ppc.c (ppc_elf_section_processing): Delete.
	(elf_backend_section_processing): Don't define.
	(ppc_elf_modify_segment_map): Set p_flags and mark valid.  Don't
	split on non-exec sections differing in SHF_PPC_VLE.  When
	splitting segments, mark size invalid.
gas/
	* config/tc-ppc.c (md_assemble): Set sh_flags for VLE.  Test
	ppc_cpu rather than calling ppc_mach to determine VLE mode.
	(ppc_frag_check, ppc_handle_align): Likewise use ppc_cpu.