test: dm: tee: extend with RPC test

test: dm: tee: extend with RPC test

Extend existing DM tee tests adding test coverage for reverse RPC calls.
Currently this commit only adds tests for I2C requests from TEE driver
to TEE supplicant, for instance reading/writing data to emulated i2c
eeprom defines in standard sandbox test device tree
(arch/sandbox/dts/test.dtb):

=> i2c bus
Bus 0:	i2c@0  (active 0)
   2c: eeprom@2c, offset len 1, flags 0
   ...

Running TEE tests:
=> ut dm tee
Test: dm_test_tee: tee.c
Test: dm_test_tee: tee.c (flat tree)
Failures: 0

Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Etienne Carriere <etienne.carriere@linaro.org>