Also support building of multiple targets with correct toolchains with
one invocation of make.

Introduce a single mangOH.sdef and remove the board/module specific
SDEFs.  The content of the single SDEF change depending on the build
parameters.  The "targets" directory was introduced based on the way
Legato handles different modules.  The location of build artifacts has
now changed.  Everything produced by the Makefile is under "build/".

The IoT slot driver has been disabled due to conflicts between it and
the way that the GPIOs for the WiFi IoT card are being configured by the
default yocto linux image.

Added the new Linux device driver for the card detect LED and
added a LED service with an API to set/get the LED status.

Removed kfree calls to free the slot memory.  The use of
devm_ calls to create the memory removes the need to call
kfree.

This member does not need to be persisted as it can simply be returned
to the caller requesting the mailbox value.

There was no point in permanently allocating the buffers since their
lifetime was function scoped and thus they could be converted to
stack variables.

Let the compiler decide what to inline

The slave_busy status doesn't need to persist, so just use a stack variable
instead.

The work queue would have been leaked in the case where the GPIO request failed
because the error handling cases were in the wrong order.

 - Remove trailing whitespace
 - Wrap lines at 80 chars
 - Format else statements according to linux coding style