spmi: Add sandbox test driver

This patch adds emulated spmi bus controller with part of
pm8916 pmic on it to sandbox and tests validating SPMI uclass.

Signed-off-by: Mateusz Kulikowski <mateusz.kulikowski@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index d69c9fc..bfc8b61 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -31,6 +31,7 @@
 CONFIG_BLK=y
 CONFIG_CLK=y
 CONFIG_SANDBOX_GPIO=y
+CONFIG_PM8916_GPIO=y
 CONFIG_SYS_I2C_SANDBOX=y
 CONFIG_CROS_EC_KEYB=y
 CONFIG_LED=y
@@ -59,6 +60,9 @@
 CONFIG_PINCTRL_SANDBOX=y
 CONFIG_DM_PMIC=y
 CONFIG_DM_PMIC_SANDBOX=y
+CONFIG_PMIC_PM8916=y
+CONFIG_SPMI=y
+CONFIG_SPMI_SANDBOX=y
 CONFIG_DM_REGULATOR=y
 CONFIG_DM_REGULATOR_SANDBOX=y
 CONFIG_RAM=y