iio: refactor info mask and ext_info attribute creation.

Introduce an enum to specify whether the attribute is separate or
shared.

Factor out the bitmap handling for loop into a separate function.

Tidy up error handling and add a NULL assignment to squish a false
positive warning from GCC.

Change ext_info shared type from boolean to enum and update in all
drivers.

Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>

include/linux/iio/iio.h

@@ -39,6 +39,11 @@ enum iio_chan_info_enum {
 	IIO_CHAN_INFO_INT_TIME,
 };
 
+enum iio_shared_by {
+	IIO_SEPARATE,
+	IIO_SHARED_BY_TYPE
+};
+
 enum iio_endian {
 	IIO_CPU,
 	IIO_BE,
@@ -58,7 +63,7 @@ struct iio_dev;
  */
 struct iio_chan_spec_ext_info {
 	const char *name;
-	bool shared;
+	enum iio_shared_by shared;
 	ssize_t (*read)(struct iio_dev *, uintptr_t private,
 			struct iio_chan_spec const *, char *buf);
 	ssize_t (*write)(struct iio_dev *, uintptr_t private,
@@ -126,7 +131,7 @@ ssize_t iio_enum_write(struct iio_dev *indio_dev,
 #define IIO_ENUM_AVAILABLE(_name, _e) \
 { \
 	.name = (_name "_available"), \
-	.shared = true, \
+	.shared = IIO_SHARED_BY_TYPE, \
 	.read = iio_enum_available_read, \
 	.private = (uintptr_t)(_e), \
 }