[sam] fixed bytes available of flash memory

Author: cmaglie

hardware/arduino/sam/boards.txt

@@ -3,7 +3,7 @@
 arduino_due_u.name=Arduino DueU Dev. Ed.
 arduino_due_u.upload.tool=bossac
 arduino_due_u.upload.protocol=sam-ba
-arduino_due_u.upload.maximum_size=49152
+arduino_due_u.upload.maximum_size=262144
 arduino_due_u.build.mcu=cortex-m3
 arduino_due_u.build.f_cpu=96000000L
 arduino_due_u.build.core=arduino
@@ -19,7 +19,7 @@ arduino_due_u.build.pid=0x003e
 arduino_due_x.name=Arduino DueX Dev. Ed.
 arduino_due_x.upload.tool=bossac
 arduino_due_x.upload.protocol=sam-ba
-arduino_due_x.upload.maximum_size=49152
+arduino_due_x.upload.maximum_size=524288
 arduino_due_x.build.mcu=cortex-m3
 arduino_due_x.build.f_cpu=84000000L
 arduino_due_x.build.core=arduino