regmap: Add missing little endian functions

This with the longer read and write masks allow supporting more
exotic devices. For example a little endian SPI device:

static const struct regmap_config foo_regmap_config = {
	.reg_bits = 16,
	.reg_stride = 4,
	.val_bits = 16,
	.write_flag_mask = 0x8000,
	.reg_format_endian = REGMAP_ENDIAN_LITTLE,
	.val_format_endian = REGMAP_ENDIAN_LITTLE,
	...
};
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/base/regmap/regmap.c

@@ -749,6 +749,9 @@ struct regmap *__regmap_init(struct device *dev,
 		case REGMAP_ENDIAN_BIG:
 			map->format.format_reg = regmap_format_16_be;
 			break;
+		case REGMAP_ENDIAN_LITTLE:
+			map->format.format_reg = regmap_format_16_le;
+			break;
 		case REGMAP_ENDIAN_NATIVE:
 			map->format.format_reg = regmap_format_16_native;
 			break;
@@ -768,6 +771,9 @@ struct regmap *__regmap_init(struct device *dev,
 		case REGMAP_ENDIAN_BIG:
 			map->format.format_reg = regmap_format_32_be;
 			break;
+		case REGMAP_ENDIAN_LITTLE:
+			map->format.format_reg = regmap_format_32_le;
+			break;
 		case REGMAP_ENDIAN_NATIVE:
 			map->format.format_reg = regmap_format_32_native;
 			break;
@@ -782,6 +788,9 @@ struct regmap *__regmap_init(struct device *dev,
 		case REGMAP_ENDIAN_BIG:
 			map->format.format_reg = regmap_format_64_be;
 			break;
+		case REGMAP_ENDIAN_LITTLE:
+			map->format.format_reg = regmap_format_64_le;
+			break;
 		case REGMAP_ENDIAN_NATIVE:
 			map->format.format_reg = regmap_format_64_native;
 			break;