PowerPC64 --plt-align

PowerPC64 --plt-align

Alignment of plt stubs was broken, firstly because the option was
being dropped due to the alignment value not being set in the "params"
struct used in elf64-ppc.c, and secondly due to not calculating the
number of alignment boundary crossings correctly.

bfd/
	* elf64-ppc.c (plt_stub_pad): Correct.
ld/
	* ld.texinfo: Correct --plt-align documentation.
	* emultempl/ppc64elf.em (plt_stub_align): Delete.  Use and set
	params.plt_stub_align instead.