EnvieM7: update usable ram size

Author: facchinm

boards.txt

@@ -64,7 +64,7 @@ envie_m7.upload.use_1200bps_touch=true
 envie_m7.upload.wait_for_upload_port=false
 envie_m7.upload.native_usb=true
 envie_m7.upload.maximum_size=786432
-envie_m7.upload.maximum_data_size=262144
+envie_m7.upload.maximum_data_size=523624
 
 
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