ipmi: put acpi.h with the other headers

Enclosing '#include <linux/acpi.h>' within '#ifdef CONFIG_ACPI' is
unnecessary, since it has its own conditional compile for CONFIG_ACPI.

Commit 0fbcf4af ("ipmi: Convert the IPMI SI ACPI handling to a
platform device") exposed this as a problem for platforms that do not
support ACPI when it introduced a call to ACPI_PTR() macro outside of
the CONFIG_ACPI conditional compile. This would have been perfectly
acceptable if acpi.h were not conditionally excluded for the non-acpi
platform, because the conditional compile within acpi.h defines
ACPI_PTR() to return NULL when compiled for non acpi platforms.

Signed-off-by: Tony Camuso <tcamuso@redhat.com>

Fixed commit reference in header to conform to standard.

Signed-off-by: Corey Minyard <cminyard@mvista.com>