Zybo Z7 board - fix MIO init issue

[Milan Obuch]

Hi,

Zybo Z7 board has two push button connected to MIO pins 50 and 51,
connecting them to Vcc1V8 when pressed, and pulldown resistors
connected to ground. These two pins are initialised with internal
pullup resistors enabled, so they are reported as 1 all the time with
no change when pressed.

Patch to fix this small issue follows. As this is my first contribution
to this project, please help me with what could be necessary to do for
this fix to be accepted, in order to fit any custom used here...

Regards,
Milan

@@ -219,8 +219,8 @@
 	EMIT_MASKWRITE(0xF80007BC, 0x00003F01U, 0x00001201U),
 	EMIT_MASKWRITE(0xF80007C0, 0x00003FFFU, 0x000012E0U),
 	EMIT_MASKWRITE(0xF80007C4, 0x00003FFFU, 0x000012E1U),
-	EMIT_MASKWRITE(0xF80007C8, 0x00003FFFU, 0x00001200U),
-	EMIT_MASKWRITE(0xF80007CC, 0x00003FFFU, 0x00001200U),
+	EMIT_MASKWRITE(0xF80007C8, 0x00003FFFU, 0x00000200U),
+	EMIT_MASKWRITE(0xF80007CC, 0x00003FFFU, 0x00000200U),
 	EMIT_MASKWRITE(0xF80007D0, 0x00003FFFU, 0x00001280U),
 	EMIT_MASKWRITE(0xF80007D4, 0x00003FFFU, 0x00001280U),
 	EMIT_MASKWRITE(0xF8000830, 0x003F003FU, 0x002F0037U),