flash/nor/stm32h7x: remove options cache and some driver enhancements

functions managing option bytes cache (stm32x_read/write_options)
have bee removed, and a new functions to modify a single option byte
have been introduced (stm32x_write/modify_option).

by the way, some helpers have been introduced to access flash registers:
  - stm32x_read_flash_reg(bank, offset, *value): int
  - stm32x_write_flash_reg(bank, offset, value): int

and a new commands to read and write a single flash option register:
  - stm32h7x option_read <bank> <option_reg offset>
  - stm32h7x option_write <bank> <option_reg offset> <value> [mask]

also lock and unlock handlers' have been reduced by using the same routine
(stm32x_set_rdp) and have been optimized to not write options unless
there is a change in RDP level.

finally, several functions have been fixed to lock flash / options in case
of failure.

Change-Id: I75057949ab9f5b4e0f602bafb76f9f80d53a522b
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: http://openocd.zylin.com/5293
Tested-by: jenkins
Reviewed-by: Christopher Head <chead@zaber.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

doc/openocd.texi

@@ -6769,6 +6769,37 @@ The @var{num} parameter is a value shown by @command{flash banks}.
 Mass erases the entire stm32h7x device.
 The @var{num} parameter is a value shown by @command{flash banks}.
 @end deffn
+
+@deffn Command {stm32h7x option_read} num reg_offset
+Reads an option byte register from the stm32h7x device.
+The @var{num} parameter is a value shown by @command{flash banks}, @var{reg_offset}
+is the register offset of the option byte to read from the used bank registers' base.
+For example: in STM32H74x/H75x the bank 1 registers' base is 0x52002000 and 0x52002100 for bank 2.
+
+Example usage:
+@example
+# read OPTSR_CUR
+stm32h7x option_read 0 0x1c
+# read WPSN_CUR1R
+stm32h7x option_read 0 0x38
+# read WPSN_CUR2R
+stm32h7x option_read 1 0x38
+@end example
+@end deffn
+
+@deffn Command {stm32h7x option_write} num reg_offset value [reg_mask]
+Writes an option byte register of the stm32h7x device.
+The @var{num} parameter is a value shown by @command{flash banks}, @var{reg_offset}
+is the register offset of the option byte to write from the used bank register base,
+and @var{reg_mask} is the mask to apply when writing the register (only bits with a '1'
+will be touched).
+
+Example usage:
+@example
+# swap bank 1 and bank 2 in dual bank devices, by setting SWAP_BANK_OPT bit in OPTSR_PRG
+stm32h7x option_write 0 0x20 0x8000000 0x8000000
+@end example
+@end deffn
 @end deffn
 
 @deffn {Flash Driver} stm32lx