Add openocd macros to write image A or B
Add openocd macros to write image A or B

These are faster than writing the entire EC, and safer if you're
mucking with things like the clock config.  Of course, if you're
changing verified boot or something else that happens before
vboot_init(), these new commands won't help, and you should keep using
the existing flash_link command.

Signed-off-by: Randall Spangler <rspangler@chromium.org>

BUG=none
TEST=manual from openocd
- Compile a new image
- From openocd, flash_link_b
- From ec console, note build compile date in image A: shouldn't have changed
- From ec consle, sysjump b; compile date should be for your new image

Change-Id: Ifd6aabe963948d3c5da5bdeb78c5f962a0f9f857

md5555/ec,mtk09422/chromiumos-platform-ec,fourier49/BIZ_EC,mtk09422/chromiumos-platform-ec,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BIZ_EC,fourier49/BIZ_EC,alterapraxisptyltd/chromium-ec,md5555/ec,alterapraxisptyltd/chromium-ec,mtk09422/chromiumos-platform-ec,longsleep/ec,akappy7/ChromeOS_EC_LED_Diagnostics,thehobn/ec,fourier49/BZ_DEV_EC,fourier49/BZ_DEV_EC,alterapraxisptyltd/chromium-ec,alterapraxisptyltd/chromium-ec,coreboot/chrome-ec,coreboot/chrome-ec,longsleep/ec,akappy7/ChromeOS_EC_LED_Diagnostics,gelraen/cros-ec,eatbyte/chromium-ec,coreboot/chrome-ec,fourier49/BZ_DEV_EC,akappy7/ChromeOS_EC_LED_Diagnostics,longsleep/ec,fourier49/BZ_DEV_EC,eatbyte/chromium-ec,thehobn/ec,gelraen/cros-ec,mtk09422/chromiumos-platform-ec,gelraen/cros-ec,coreboot/chrome-ec,longsleep/ec,md5555/ec,eatbyte/chromium-ec,eatbyte/chromium-ec,thehobn/ec,coreboot/chrome-ec,coreboot/chrome-ec,md5555/ec,thehobn/ec,gelraen/cros-ec,fourier49/BIZ_EC