nrf51: implement soft reset and hard reset
nrf51: implement soft reset and hard reset

TEST=manual test with the console command.  Reset flags are set correctly.
BRANCH=NONE
BUG=None

Change-Id: I3ea4301206be6fe4e79a4b49c002c020980c516d
Signed-off-by: Myles Watson <5fb4cec39c2b8f78857f7951c3db11d932932621@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/242901
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

fourier49/BZ_DEV_EC,md5555/ec,coreboot/chrome-ec,md5555/ec,md5555/ec,fourier49/BIZ_EC,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BZ_DEV_EC,fourier49/BZ_DEV_EC,coreboot/chrome-ec,eatbyte/chromium-ec,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BZ_DEV_EC,eatbyte/chromium-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BIZ_EC,eatbyte/chromium-ec,md5555/ec,fourier49/BIZ_EC,coreboot/chrome-ec,coreboot/chrome-ec,fourier49/BIZ_EC,coreboot/chrome-ec,eatbyte/chromium-ec,akappy7/ChromeOS_EC_LED_Diagnostics