PATCH LD octets vs byte support, revised

[Timothy Wall]

This patch supersedes the previous one, incorporating Ian's comments on
BYTE behavior for targets where a byte is greater than one octet.

* ld/ld.texinfo:   Updated description of BYTE, SHORT, LONG, etc to be
clear about behavior when an octet is smaller than one byte.
* ld/ldlang.c (lang_do_assignments, lang_size_sections):  Use the larger
of the directive size or octets_per_byte for the number of octets
allocated in the output section.