spd.[ch]: reduce scope of various things

Reduce the scope of some function prototypes, macros and variables where
easily possible.
No functional change intended.

Change-Id: I7f2838f49ebd39a4ce0c1fb43b9add65024fea89
Signed-off-by: Stefan Tauner <stefan.tauner@gmx.at>
Reviewed-on: https://review.coreboot.org/28218
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
2 files changed