drivers: Add SPMI bus uclass

Qualcom processors use proprietary bus to talk with PMIC devices -
SPMI (System Power Management Interface).
On wiring level it is similar to I2C, but on protocol level, it's
multi-master and has simple autodetection capabilities.
This commit adds simple uclass that provides bus read/write interface.

Signed-off-by: Mateusz Kulikowski <mateusz.kulikowski@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/spmi/Kconfig b/drivers/spmi/Kconfig
new file mode 100644
index 0000000..0b9bd31
--- /dev/null
+++ b/drivers/spmi/Kconfig
@@ -0,0 +1,10 @@
+menu "SPMI support"
+
+config SPMI
+	bool "Enable SPMI bus support"
+	depends on DM
+	---help---
+	  Select this to enable to support SPMI bus.
+	  SPMI (System Power Management Interface) bus is used
+	  to connect PMIC devices on various SoCs.
+endmenu