console: allocate ring buffer earlier

... when "conring_size=" was specified on the command line. We can't
really do this as early as we would want to when the option was not
specified, as the default depends on knowing the system CPU count. Yet
the parsing of the ACPI tables is one of the things that generates a
lot of output especially on large systems.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com> (ARM and generic bits)
Release-Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>