boot: zephyr: Fix pyocd board runner args

The pyocd runner in zephyr changed its arguments slightly when it
converted to the new unified pyocd tool with subcommands. Change the
board runner args here similarly so we can use 'west flash' again for
the zephyr bootloader.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>
diff --git a/boot/zephyr/CMakeLists.txt b/boot/zephyr/CMakeLists.txt
index 6050e0d..470103c 100644
--- a/boot/zephyr/CMakeLists.txt
+++ b/boot/zephyr/CMakeLists.txt
@@ -52,7 +52,7 @@
 macro(app_set_runner_args)
   if(CONFIG_ZEPHYR_TRY_MASS_ERASE)
     board_runner_args(dfu-util "--dfuse-modifiers=force:mass-erase")
-    board_runner_args(pyocd "--flashtool-opt=-ce")
+    board_runner_args(pyocd "--flash-opt=-e=chip")
     board_runner_args(nrfjprog "--erase")
   endif()
 endmacro()