rpmsg: Remove usage of the deprecated ida_simple_xx() API

ida_alloc() and ida_free() should be preferred to the deprecated
ida_simple_get() and ida_simple_remove().

Note that the upper limit of ida_simple_get() is exclusive, but the one of
ida_alloc_max() is inclusive. So a -1 has been added when needed.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/c09ee5b66d451bf97d14c167048549aa0824ee06.1705225049.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>