flash/stm32lx: mention explicitly that this driver covers STM32 L0 and L1

flash/stm32lx: mention explicitly that this driver covers STM32 L0 and L1

this is to avoid confusion with STM32 L4, L4+ and L5 families

also:
 - a warning message is changed to error
 - stm32l0x and stm32l1x aliases has been created to permit
   the usage of either names

Change-Id: If3f16d2a3b7d1369959aa7407da37a9076ea91d7
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: http://openocd.zylin.com/5437
Reviewed-by: Marc Schink <dev@zapb.de>
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>