docs: samples: Update pyocd calls to unified tool subcommands

pyocd 0.14.0 merged its command-line tools into a unified pyocd tool
with subcommands. The separate command-line tools still remain, but are
deprecated. Update all pyocd calls in samples and documentation to use
the new unified pyocd tool with subcommands.

Note that pyocd 0.15.0 has an issue with the command 'pyocd erase',
which was fixed in pyocd 0.16.0.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>
diff --git a/docs/testplan-mynewt.md b/docs/testplan-mynewt.md
index 0b16fd4..5a227b9 100644
--- a/docs/testplan-mynewt.md
+++ b/docs/testplan-mynewt.md
@@ -150,8 +150,8 @@
 
 * Mass erase MCU
 
-        $ pyocd-flashtool -ce
+        $ pyocd erase --chip
 
 * Flashing image in slot 1:
 
-        $ pyocd-flashtool -se --address 0x80000 ${IMG_FILE} bin
+        $ pyocd flash -e sector -a 0x80000 ${IMG_FILE} bin