SYS_TICK: Use Timer2 instead of Timer0.

Downside of Timer0 is, we have to manually reload
the timer value. Timer2 can do that automaticly.
This saves a lot of time in the interrupt-handler
of the Timer.

Currently Timer2 is used for baudrate-generation
but in a separete commit this is moved to Timer1.

crtstart.asm

@@ -16,12 +16,12 @@ __interrupt_vect:
 	.ds     5
 	ljmp	_isr_ext1	; 0x13
 	.ds     5
-	reti
+	reti			; 0x1b TIMER 1 IRQ
 	.ds     7
  	ljmp    _isr_serial	; 0x23
 	.ds     5
-	reti			; 0x2b TIMER 2 IRQ
-	.ds     7
+	ljmp	_isr_timer2	; 0x2b TIMER 2 IRQ
+	.ds     5
 	reti			; 0x33 NOT used by DW8051
 	.ds     7
 	reti			; 0x3b Serial port 1 RX/TX IRQ