flash/stm32l4x: enhance protect handler to use efficiently all WRP areas

flash/stm32l4x: enhance protect handler to use efficiently all WRP areas

stm32l4_protect: was using one WRP area per bank, without checking
if it is already protecting some sectors.
protection algo is more complicated than that, before using a WRP area
we should check if it is already used, then either reuse it for extension
(or reduction) or use a free area.

introduce a new command: stm32l4x wrp_info bank_num ['bank1'|'bank2']
this command lists the protected areas using WRP.

Note: for some devices like STM32L4R/S in single bank mode, all 4 WRP areas
are usable for that bank, to manage this case an attribute 'use_all_wrpxx'
was introduced into stm32l4_part_info and used later in protection handlers

example usage:
	$ telnet localhost 4444
	> flash probe 0
	  device idcode = 0x10036470 (STM32L4R/L4Sxx - Rev: Y)
	  flash size = 2048kbytes
	  flash mode : dual-bank
	  flash 'stm32l4x' found at 0x08000000
	> stm32l4x wrp_info 0
	  no protected areas
	> flash protect 0 0 4 on
	  set protection for sectors 0 through 4 on flash bank 0
	> flash protect 0 8 9 on
	  set protection for sectors 8 through 9 on flash bank 0
	> stm32l4x wrp_info 0
	  protected areas: [0,4][8,9]
	> flash protect 0 6 6 on
	  the device WRPxy are not enough to set the requested protection
	  failed setting protection for blocks 6 to 6
	> flash protect 0 3 5 on
	  set protection for sectors 3 through 5 on flash bank 0
	> stm32l4x wrp_info 0
	  protected areas: [0,5][8,9]
	> flash protect 0 6 7 on
	  set protection for sectors 6 through 7 on flash bank 0
	> stm32l4x wrp_info 0
	  protected areas: [0,9]
	> flash protect 0 5 6 off
	  cleared protection for sectors 5 through 6 on flash bank 0
	> stm32l4x wrp_info 0
	  protected areas: [0,4][7,9]

Change-Id: I42bd84fa66edd93406e18c6d89310faa5267ffa7
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: http://openocd.zylin.com/6107
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>