mfd: ssbi: Add regmap read/write helpers

Add read and write helper functions that the pm8921-core driver
can use to read and write ssbi registers via a "no-bus" regmap.
Signed-off-by: NStephen Boyd <sboyd@codeaurora.org>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

include/linux/ssbi.h

@@ -20,4 +20,24 @@
 int ssbi_write(struct device *dev, u16 addr, const u8 *buf, int len);
 int ssbi_read(struct device *dev, u16 addr, u8 *buf, int len);
 
+static inline int
+ssbi_reg_read(void *context, unsigned int reg, unsigned int *val)
+{
+	int ret;
+	u8 v;
+
+	ret = ssbi_read(context, reg, &v, 1);
+	if (!ret)
+		*val = v;
+
+	return ret;
+}
+
+static inline int
+ssbi_reg_write(void *context, unsigned int reg, unsigned int val)
+{
+	u8 v = val;
+	return ssbi_write(context, reg, &v, 1);
+}
+
 #endif