Changed 1284p fuse setting for 8, 16 and 20 Mhz

Symtopns:

- X axis move in one direction
- limit switches fail to trigger
- unable to reprogram the device via bootloader
- stops working when the reset switch is pressed.
- device fails to bootup when power by a slow raise power supply.

Solution:
- Disabled the jtag
- set the correct clock selection bit
- set the correct bootloader memory size
- enable brown-out setting
- enable clock power up delay
Merge pull request #741 from Opticalworm/Marlin_v1

Changed 1284p fuse setting for 8, 16 and 20 Mhz