tools/metrics.py: Add VIRT_RV32 to the code size metrics.

This commit adds the Qemu-based RISC-V 32 bits `VIRT_RV32` board to the
list of ports/boards to be built for measuring code size changes.

Signed-off-by: Alessandro Gatti <a.gatti@frob.it>

tools/metrics.py

@@ -71,6 +71,7 @@ port_data = {
     "r": PortData("nrf", "nrf", "build-PCA10040/firmware.elf"),
     "p": PortData("rp2", "rp2", "build-RPI_PICO_W/firmware.elf", "BOARD=RPI_PICO_W"),
     "d": PortData("samd", "samd", "build-ADAFRUIT_ITSYBITSY_M4_EXPRESS/firmware.elf"),
+    "v": PortData("qemu rv32", "qemu", "build-VIRT_RV32/firmware.elf", "BOARD=VIRT_RV32"),
 }