mini51: support for Nuvoton NuMicro Mini51 series flash memory

mini51: support for Nuvoton NuMicro Mini51 series flash memory

Adds a flash driver for Nuvoton MINI51, MINI52 and MINI54 microcontrollers.

At the moment, it only supports the erase and write operations.

These microcontrollers have a 4 / 8 / 16 KB APROM for application code and a
2 KB LDROM for bootloaders. When the MCU has booted off the APROM, the LDROM
isn't mapped in memory but can be programmed, and the other way around.
This means that the ARM core is typically rebooted for programming. After a
successful write or erase operation, it is rebooted again, using the initial
boot source.

This driver only supports programming the APROM.

This driver is a pure JTAG implementation, it doesn't use any SRAM.

I've tested it on a MINI54ZAN microcontroller using an ST-LINK/V2. With the
microcontroller running at the default clock frequency of 22.1184 MHz, speed
seems to be around 1.1 KB/s.

Change-Id: I180889c55af9fb5614cd99a953b755baba14288a
Signed-off-by: Cosmin Gorgovan <cosmin@linux-geek.org>
Reviewed-on: http://openocd.zylin.com/1546
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>