Add ARMv7-M architecture support

The framework relies on some code specific to the
architecture of the processor it is running on. This
patch adds the code specific to the ARMv7-M based
processors.

Co-authored-by: Filipe Rinaldi <filipe.rinaldi@arm.com>
Co-authored-by: Paul Beesley <paul.beesley@arm.com>
Co-authored-by: Chris Kay <chris.kay@arm.com>
Co-authored-by: Elieva Pignat <elieva.pignat@arm.com>
Co-authored-by: Pedro Custodio <pedro.krewinkelcustodio@arm.com>

Change-Id: If60f7f6a8907336bca90fe01394dab586b5c9a42
Signed-off-by: Ronald Cron <ronald.cron@arm.com>