Use direct hardware access for internal requests for KCS and SMIC.

[jhb]

Summary

• 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().

Test Plan

Have not yet run this anywhere. We should probably not enable the
watchdog when using SSIF.

[jhb]

• Zero a driver request structure when it is reused.

[jhb]

• Merge branch 'master' into ipmi_kernel_direct