regmap/adi_regmap_common.txt: Add missing RD_RAW_DATA field

Author: alin724

docs/regmap/adi_regmap_common.txt

@@ -137,6 +137,13 @@ EXT_SYNC
 RO
 If set the transport layer cores (ADC/DAC) have implemented the support for external synchronization signal.
 ENDFIELD
+
+FIELD
+[13] 0x0
+RD_RAW_DATA
+If set, the ADC has the capability to read raw data in register REG_CHAN_RAW_DATA from adc_channel.
+ENDFIELD
+
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