Remove the now-unused armv7m_init() function. This was a legacy from
before we properly QOMified ARMv7M, and it has some flaws:

 * it combines work that needs to be done by an SoC object (creating
   and initializing the TYPE_ARMV7M object) with work that needs to
   be done by the board model (setting the system up to load the ELF
   file specified with -kernel)
 * TYPE_ARMV7M creation failure is fatal, but an SoC object wants to
   arrange to propagate the failure outward
 * it uses allocate-and-create via qdev_create() whereas the current
   preferred style for SoC objects is to do creation in-place

Board and SoC models can instead do the two jobs this function
was doing themselves, in the right places and with whatever their
preferred style/error handling is.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20180601144328.23817-3-peter.maydell@linaro.org