print.c: Move list of known boards to known_boards.c

This free's up namespace pollution and a layer of ifdef.

BUG=b:242246291
TEST=builds

Change-Id: Id098343b9b79fd9b01c7dc48e64756ad350f9d83
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/66720
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Thomas Heijligen <src@posteo.de>

meson.build

@@ -268,6 +268,7 @@ if config_internal
     'chipset_enable.c',
     'internal.c',
     'processor_enable.c',
+    'known_boards.c',
   )
   if host_is_x86
     srcs += files(