ion: unmapped heap support in ion dummy driver **not for mainline**

ion: unmapped heap support in ion dummy driver **not for mainline**

Add configuration ION_DUMMY_UNMAPPED_HEAP to enable optional definition
of a statically defined "unmapped" heap for test purpose: kernel config
must provide the memory pool base address and byte size.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
(cherry picked from commit 961993fde60ebd06715d1433f8eb265471a0f38c
 linaro repo https://github.com/linaro-swg/linux.git
 tag optee-v4.9-20171005)