Kinetis: Add K24 support and tidy up

The K24 uses the KL-style SDID register and has some flashing quirks, so the kinetis driver does not support it properly.
Extend the chip detection routine to support the new SDID format. Add a parameter for the maximum flash size, as the K24 only supports 1k flashing blocks but has 4k sector size. Remove global 'granularity' array, as it's only really needed in one function. Replace 'klxx' with an enum showing which flash commands are actually supported on a given chip.

Signed-off-by: Patrick Stewart <patstew@gmail.com>
Change-Id: Ie244fab564d58c5cfe4fa36a025f0b2674ffad69
Reviewed-on: http://openocd.zylin.com/2864


Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-by: Paul Fertser <fercerpav@gmail.com>