regmap: Add provisions to have user-defined read operation

This commit is a preparatory commit to provide "no-bus" configuration
option for regmap API. It adds necessary plumbing needed to have the
ability to provide user define register read function.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
diff --git a/drivers/base/regmap/internal.h b/drivers/base/regmap/internal.h
index 401d191..471eb90 100644
--- a/drivers/base/regmap/internal.h
+++ b/drivers/base/regmap/internal.h
@@ -74,6 +74,8 @@
 	const struct regmap_access_table *volatile_table;
 	const struct regmap_access_table *precious_table;
 
+	int (*reg_read)(void *context, unsigned int reg, unsigned int *val);
+
 	u8 read_flag_mask;
 	u8 write_flag_mask;