zephyr-flash-bossac.bbclass: Use internal bossac tool instead looking up PATH

Instead of looking in PATH on the host to find bossac we now depend on the
native variant we build and set the path to our yocto build tool.

Closes: https://git.ostc-eu.org/OSTC/planning/core-os/-/issues/240



Signed-off-by: Stefan Schmidt <stefan.schmidt@huawei.com>

classes/zephyr-flash-bossac.bbclass

 #@DESCRIPTION: class file to flash boards like Arduino Nano BLE which depends on bossac for flashing
 
+DEPENDS += "bossa-native"
+
 python do_flash_usb() {
     import shutil
     import subprocess
     import serial.tools.list_ports
 
-    # Note: make sure the installed bossac is set to PATH before running flash_usb()
     # Check if bossac is avaiable for flashing
-    origbbenv = d.getVar("BB_ORIGENV", False)
-    bossac_path = shutil.which("bossac", path=origbbenv.getVar('PATH'))
+    bossac_path = shutil.which("bossac")
 
     if not bossac_path:
-       bb.fatal("ERROR: bossac not found, please install first and add to PATH")
+       bb.fatal("ERROR: bossac not found.")
 
     board = d.getVar('BOARD')
 
@@ -47,4 +47,3 @@ python do_flash_usb() {
 addtask do_flash_usb after do_deploy
 
 do_flash_usb[nostamp] = "1"
-do_flash_usb[vardepsexclude] = "BB_ORIGENV"