qemu_template.sh: Allow parameters for VM pflash firmware

The qemu UEFI and regular qemu script only differ by having a default
value for the firmware. If one tries to switch between different
firmwares one normally would modify the script.
Make it easier to switch boot modes and use custom firmwares by
supporting a flag to set the pflash contents.

build_library/qemu_template.sh

@@ -31,6 +31,8 @@ Options:
     -M MB       Set VM memory in MBs.
     -T DIR      Add a software TPM2 device through swtpm which stores secrets
                 and the control socket to the given directory.
+    -R FILE     Set up pflash ro content, e.g., for UEFI (with -W).
+    -W FILE     Set up pflash rw content, e.g., for UEFI (with -R).
     -s          Safe settings: single simple cpu and no KVM.
     -h          this ;-)
 
@@ -90,6 +92,12 @@ while [ $# -ge 1 ]; do
         -T|-tpm)
             SWTPM_DIR="$2"
             shift 2 ;;
+        -R|-pflash-ro)
+            VM_PFLASH_RO="$2"
+            shift 2 ;;
+        -W|-pflash-rw)
+            VM_PFLASH_RW="$2"
+            shift 2 ;;
         -v|-verbose)
             set -x
             shift ;;