otp_tool: Use a default baudrate.
otp_tool: Use a default baudrate.

Use a default baudrate of 500000. Update all the APIs
to pass in an option to use a different baudrate if desired.

Signed-off-by: Naveen Kaje <79e427f88b1293e6ef90566b3bd0a85565336125@juul.com>

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core