env/windows-arm64/aws: increase VM resources

a1.metal instances have 32Gb of ram, and 16 cores. We should try to use
as much as possible.

We run into CLOCK_WATCHDOG_TIMEOUT when using more than 4 of the 16
cores. The VM can also fail to boot. We have a thread discussing how to
resolve this.

A new AMI will need to be created and configured after any changes to
this script.

For golang/go#42604

Change-Id: If49b89718fca6dc5cee30e609a8ded9f99bf1f05
Reviewed-on: https://go-review.googlesource.com/c/build/+/322655
Trust: Alexander Rakoczy <alex@golang.org>
Run-TryBot: Alexander Rakoczy <alex@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>

env/windows-arm64/aws/win10-arm64.sh

@@ -10,7 +10,7 @@
   -cpu host \
   --accel kvm \
   -smp 4 \
-  -m 8G \
+  -m 24G \
   -drive file=/home/ubuntu/win10/QEMU_EFI.fd,format=raw,if=pflash,readonly=on \
   -drive file=/home/ubuntu/win10/QEMU_VARS.fd,format=raw,if=pflash \
   -device nec-usb-xhci \