x86: Define PLT_CIE_LENGTH and PLT_FDE_* in elfxx-x86.h

x86: Define PLT_CIE_LENGTH and PLT_FDE_* in elfxx-x86.h

Since PLT_CIE_LENGTH, PLT_FDE_LENGTH, PLT_FDE_START_OFFSET and
PLT_FDE_LEN_OFFSET are identical in elf32-i386.c and elf64-x86-64.c,
they can be defined in elfxx-x86.h.

	* elf32-i386.c (PLT_CIE_LENGTH, PLT_FDE_LENGTH,
	PLT_FDE_START_OFFSET, PLT_FDE_LEN_OFFSET): Moved to ...
	* elfxx-x86.h (PLT_CIE_LENGTH, PLT_FDE_LENGTH,
	PLT_FDE_START_OFFSET, PLT_FDE_LEN_OFFSET): Here.
	* elf64-x86-64.c (PLT_CIE_LENGTH, PLT_FDE_LENGTH,
	PLT_FDE_START_OFFSET, PLT_FDE_LEN_OFFSET): Removed.