ACPI / IPMI: Fix potential response buffer overflow

This patch enhances sanity checks on message size to avoid potential buffer
overflow.

The kernel IPMI message size is IPMI_MAX_MSG_LENGTH(272 bytes) while the
ACPI specification defined IPMI message size is 64 bytes.  The difference
is not handled by the original codes.  This may cause crash in the response
handling codes.

This patch closes this gap and also combines rx_data/tx_data to use single
data/len pair since they need not be seperate.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Reviewed-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>