platform: makefile: do not generate ifndef define in ram headers

platform: makefile: do not generate ifndef define in ram headers

The RAM header files are containing no definitions and only code. So
the usual structure to make one header file only include once is not
suitable for our usecase.
We need that in order to be able to handle RAM in the legacy way, there
we include those files a second time. As they also have return values
in it is not suitable to return those headers in a function.

As of this reasons remove ifndef define structure generation in
Makefile.

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
(cherry picked from commit c9721dfafea708179ff49d618954ee8064e151cc)
(cherry picked from commit 615a8f55244454071619579a07e2c59d37d1a9b5)