ACPI: Make Embedded Controller command timeout delay configurable

Here and then there show up machines which need higher timeout values.
Finding this on affected machines can be cumbersome, because
ACPI_EC_DELAY is a compile option -> make it configurable via boot param.

This can even be provided writable at runtime via:
/sys/modules/acpi/parameters/ec_delay

Known machines where this helps:
Some HP machines where for whatever reasons specific EC accesses take
very long at resume from S3 (in _WAK function).
The AE_TIME error is passed upwards and the ACPI interpreter will
not execute the rest of the _WAK function which results in not properly
initialized devices/variables with different side-effects.

Afaik, on some MSI machines this helped as well.

If this param is needed there probably are underlying problems like:
  - EC firmware bug
  - A kernel EC driver bug
  - An ACPI interpreter behavior (e.g. timings when specific
    EC accesses happen and how) which the EC does not like
  - ...
which should get evaluated further, but often are nasty or
impossible to fix from OS side.

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>