Documentation: Add doxygen_platform target

Create a doxygen target that builds documentation just for the platform
that is currently selected in Kconfig.  This gives us something that is
much more useful to most people.

Change-Id: I25c3cdac2dd383b89df6389ba9011dac913a0a9b
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/15577
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
2 files changed