Minor cleanup of shell interface

Minor cleanup

Subcomponent drivers:
 * Aquila LPC
 * Swift FSI
 * OpenCores I2C
 * SimplePWM
 * Tercel SPI

Add GPIO control command

This enables HDMI output (AST2500 DVO) when the ASpeed pinmux is
configured to DVO mode prior to AST2500 CPU deactivation.

This is to allow for future functionality which may consume
more of the console thread stack.

This resolves sporadic Zephyr crashes on Blackbird hosts
after the host enters skiboot.

This avoids switching to another task and potentially
violating timing / sequencing requirements in the process.

Test case: pressing power button instead of using obmcutil
no longer crashes Zephyr when powering on the host platform.

This fixes LPC clock start failures from the
clock buffer GPIO not being set to output mode.

This avoids a mismatch between BMC internal host state and the
actual physical state of the host if the BMC is rebooted / reloaded
while the host platform is online.

This stabilizes access pending future resolution of place and
route timing failures in the Tercel core on ECP5.

Update build command in README

Update build instructions in README

This resolves a BMC crash in late IPL (skiboot / initial kernel load)
exclusively observed on Talos II systems.