Allow 'ptype/o' for assembly

Allow 'ptype/o' for assembly

PR exp/28359 points out that 'ptype/o' does not work when the current
language is "asm".

I tracked this down to a hard-coded list of languages in typeprint.c.
This patch replaces this list with a method on 'language_defn'
instead.  If all languages are ever updated to have this feature, the
method could be removed; but in the meantime this lets each language
control what happens.

I looked at having each print_type method simply modify the flags
itself, but this doesn't work very well with the feature that disables
method-printing by default (but allows it via a flag).

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28359
Approved-By: Andrew Burgess <aburgess@redhat.com>
Approved-By: Keith Seitz <keiths@redhat.com>