flash/nor/stm32h7x: remove flash size information from device name

flash/nor/stm32h7x: remove flash size information from device name

There is no sense in displaying the max size (2M) as there is variants
of this device with reduced flash size

Change-Id: I40574064d75fdf2a038044c81038a6d7abc6c4dd
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: http://openocd.zylin.com/5288
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Christopher Head <chead@zaber.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>