gdb, gdbserver: Add missing install-dvi Makefile target

gdb, gdbserver: Add missing install-dvi Makefile target

For some reason install-dvi is missing although other targets of the
same family are present. This looks like an oversight.

This enables calling 'make install-dvi' from the top-level build
directory.

Fix what looks like another oversight: include 'pdf' in 'all-doc' in
gdb/doc/Makefile.in.

Approved-By: Luis Machado <luis.machado@arm.com>
Tested-By: Luis Machado <luis.machado@arm.com>