Add support for relocating function pointers.

This patch adds a new relocation type for EPIPHANY: BFD_RELOC_EPIPHANY_OVER32.
It adds support for building C code with `-fpic` such as:

~~~
int foo = 0;
void a()
{
  foo++;
}
void (*b)() = a;
~~~

With `b` compiling down to:

~~~
_b:
  .word _a@PLT
~~~

bfd/
	* reloc.c (BFD_RELOC_EPIPHANY_OVER32): Define a new PLT
	relocation.
	* libbfd.h: Regenerate.
	* bfd-in2.h: Regenerate.
	* elf32-epiphany.c (epiphany_elf_howto_table): Add a 32 bit PLT
	relocation: R_EPIPHANY_OVER32.
	(epiphany_reloc_type_lookup): Likewise.
	(epiphany_final_link_relocate): Handle PLT relocation of type
	R_EPIPHANY_OVER32.
	(epiphany_elf_check_relocs): Add R_EPIPHANY_OVER32 to the
	relocation types that need a PLT entry.

gas/
	* config/tc-epiphany.h (TC_PARSE_CONS_EXPRESSION): Define.
	(TC_CONS_FIX_NEW): Likewise.
	* config/tc-epiphany.c (epiphany_parse_cons_expression): New
	function.
	(epiphany_cons_fix_new): New function.

include/
	* elf/epiphany.h (R_EPIPHANY_OVER32): Define.