tcl: stm32mp15x: add target and board config files

tcl: stm32mp15x: add target and board config files

The stm32mp15x has one or two Cortex-A7 (depending on the P/N) and
one Cortex-M4.
The second core is automatically detected by the target script.
In "engineering boot" all the cores are accessible.
In "production boot" the Cortex-M4 is kept in reset state after
power-on or NRST.

The board DK2 includes a ST-Link/V2, but only SWD is connected.

Change-Id: Ib6ebefcc696b1716e0f98694cadf0b04fd7d11d6
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5454
Tested-by: jenkins
Reviewed-by: Oleksij Rempel <linux@rempel-privat.de>