allwinnerA20: switch to the ARM generic timer

The memory mapping for the timer only uses 1K on AllwinnerA20, but
the minimum device mapping is 4K in seL4. Other devices within this
4K page (CCU and PIO) cannot be accessed in the userland.
Replace the kernel timer with the ARM generic timer on AllwinnerA20,
and remove the implementation for AllwinnerA20 specific timer in the
kernel. So we should have user access to those devices now.

Signed-off-by: Luca (Wei) Chen <wei@cvluca.com>

tools/hardware.yml

@@ -128,19 +128,6 @@ devices:
         index: 3
         undef_index: 2
       INTERRUPT_VTIMER_EVENT: 2
-  # Allwinner A10 Timer (timer/allwinner,sun4i-timer.txt)
-  - compatible:
-      - allwinner,sun4i-a10-timer
-    regions:
-      - index: 0
-        kernel: TIMER0_PPTR
-    interrupts:
-      # A20 also has the ARM architected timer,
-      # but we want to use the allwinner timer
-      # for now at least.
-      KERNEL_TIMER_IRQ:
-        index: 0
-        priority: 1
   # ARM per-core timer-watchdog (timer/arm,twd.txt)
   - compatible:
       - arm,cortex-a9-twd-timer