espi-control: Add program to disable eSPI

This commit introduces a program that can disable and re-enable eSPI on
a Nuvoton BMC.

Tested:
- Ran "npcm7xx_espi_control -d", and confirmed that IPMI stopped
  working.
- Ran "npcm7xx_espi_control", and confirmed that IPMI started working
  again.

Change-Id: I9637ac4d84b82931f107946ff53e7ef16a965d25
Signed-off-by: John Wedig <johnwedig@google.com>
5 files changed