PowerPC readonly_dynrelocs

PowerPC64 lacked the mapfile textrel warning on finding dynamic relocs
in read-only sections.  This patch adds it, and tidies the
readonly_dynrelocs interface.  PowerPC doesn't need a SEC_ALLOC test
because !SEC_ALLOC sections are excluded by check_relocs so will never
have dyn_relocs.

	* elf32-ppc.c (readonly_dynrelocs): Delete info param.  Update all
	callers.  Don't bother with SEC_ALLOC test.  Return section pointer.
	Move minfo call to..
	(maybe_set_textrel): ..here.
	* elf64-ppc.c (readonly_dynrelocs): Return section pointer.
	(maybe_set_textrel): Call minfo to print textrel warning to map file.