rmodules: use rmodtool to create rmodules

Start using the rmodtool for generating rmodules.
rmodule_link() has been changed to create 2 rules:
one for the passed in <name>, the other for creating
<name>.rmod which is an ELF file in the format of
an rmodule.

Since the header is not compiled and linked together
with an rmodule there needs to be a way of marking
which symbol is the entry point. __rmodule_entry is
the symbol used for knowing the entry point. There
was a little churn in SMM modules to ensure an
rmodule entry point symbol takes a single argument.

Change-Id: Ie452ed866f6596bf13f137f5b832faa39f48d26e
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/5379
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)