doc: fix warnings "Error when parsing function declaration." due to __deprecated

Sphinx's parser gets all confused; add a workaround using @fn,
document the workaround in the contribution section; bug filed with
Sphinx for a permanent sollution.

Change-Id: I0200add092da27206b9d006bb13110c4cc37d0e4
Signed-off-by: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
3 files changed