cmd: optee_rpmb: build cmd for sandbox

Support CMD_OPTEE_RPMB for SANDBOX configurations.
Test:

$ ./u-boot -d arch/sandbox/dts/test.dtb
...
=> optee_rpmb write_pvalue test_variable test_value
Wrote 11 bytes
=> optee_rpmb read_pvalue test_variable 11
Read 11 bytes, value = test_value

Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Signed-off-by: Igor Opaniuk <igor.opaniuk@gmail.com>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 8eeb99e..9dd90da 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1348,7 +1348,9 @@
 
 config CMD_OPTEE_RPMB
 	bool "Enable read/write support on RPMB via OPTEE"
-	depends on SUPPORT_EMMC_RPMB && OPTEE
+	depends on (SUPPORT_EMMC_RPMB && OPTEE) || SANDBOX_TEE
+	default y if SANDBOX_TEE
+	select OPTEE_TA_AVB if SANDBOX_TEE
 	help
 	  Enable the commands for reading, writing persistent named values
 	  in the Replay Protection Memory Block partition in eMMC by