[uart] Add first pass UART driver and logger

First attempt at a UART driver. I'm not sure it's the most stable. Now
that userspace is handling displaying logs, also removed serial and log
output support from the kernel.

assets/manifests/default.yaml

@@ -6,4 +6,4 @@ programs:
     flags: panic
   - name: drv.uefi_fb
     flags: graphical
-  - name: testapp
+  - name: drv.uart