flash/nor/stm32f1x: Add support for GD32F1x0/3x0

flash/nor/stm32f1x: Add support for GD32F1x0/3x0

Nowadays, when it's difficult to buy STM32F030,
the use of GD32F130 seems to be an interesting functional alternative.
This is cortex-M3 and it works with the stm32f1x driver, but unfortunately not fully.
The main difference is another offset of user option bits
(like WDG_SW, nRST_STOP, nRST_STDBY) in option byte register
(FLASH_OBR/FMC_OBSTAT 0x4002201C).
Any use of functions like lock or unlock results in change default values of the those bits stored in flash.
Thus broken microcontroller is malfunctioning, e.g. flash block programming is interrupted
by unexpected active hardware watchog (after 0.4s).
This patch is a simplified version of #4592 done by Dominik Peklo (http://openocd.zylin.com/#/c/4592/).
GigaDevice GD32F1x0 & GD32F3x0 series devices share DEV_ID
with STM32F101/2/3 medium-density line,
however they use a REV_ID different from any STM32 device,
so can be succesfully detected.

Change-Id: I252cdf738d94983b70676a3497326f90c329e292
Signed-off-by: asier70Andrzej Sierżęga <asier70@gmail.com>
Reviewed-on: http://openocd.zylin.com/6164
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>