parallel.c: Consoldiate parallel master registration logic

This is analogous to spi.c and opaque.c however parallel
logic was previously never consoldiated.

This free's up flashrom.c from namespace pollution.

Tested: builds with both make and meson.

Change-Id: Ie08e2e6c51ccef5281386bf7e3df439b91573974
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/66651
Original-Reviewed-by: Thomas Heijligen <src@posteo.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72349
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/meson.build b/meson.build
index 4acecf6..67c6c01 100644
--- a/meson.build
+++ b/meson.build
@@ -94,6 +94,7 @@
   'layout.c',
   'libflashrom.c',
   'opaque.c',
+  'parallel.c',
   'print.c',
   'programmer.c',
   'programmer_table.c',