MFC 278321:

MFC 278321:
Use direct hardware access for internal requests for KCS and SMIC.  In
particular, updates to the watchdog should no longer sleep.
- Add a new IPMI_IO_LOCK for low-level I/O access.  Use this for
  kcs_polled_request() and smic_polled_request().
- Add a new backend callback "ipmi_driver_request" to handle a driver
  request.  The new callback performs the request sychronously for KCS
  and SMIC.  SSIF still defers the work to the worker thread since the
  worker thread sleeps during request processing anyway.
- Allocate driver requests on the stack rather than using malloc().

git-svn-id: svn://svn.freebsd.org/base/stable/8@279964 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f