AdvancedFeaturePkg/Ipmi: Fix GCC Build Failures

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2059



These build failures can be reproduced simply by building the
AdvancedFeaturePkg.dsc file in GCC5. To build the whole package
DSC (not pull individual features into other packages), set
the WORKSPACE variable to the edk2 directory in the workspace
as is done by executing edksetup.sh then create the PACKAGES_PATH
variable and add the Platform/Intel and Silicon/Intel directories
to the variable value. Then start the build of AdvancedFeaturePkg.dsc:
  'build -p AdvancedFeaturePkg/AdvancedFeaturePkg.dsc'

This change corrects the following issues reported by GCC:
  * BmcAcpi.c - Cast the pointer actual parameter types passed to
                functions to the formal parameter type.
  * OsWdt.c - Return the Status variable as the function return value
              in DriverInit ().
  * PeiIpmiInit.c - Return the Status variable as the function return
                    value in PeimIpmiInterfaceInit ()
  * SolStatus.c - Remove the unused variable SOLEnabled. The variable
                  was not removed after a code refactoring.

All future contributions to AdvancedFeaturePkg must successfully build
in GCC after this change.

Cc: Dandan Bi <dandan.bi@intel.com>
Cc: Sai Chaganty <rangasai.v.chaganty@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Michael Kubacki <michael.a.kubacki@intel.com>
Reviewed-by: Sai Chaganty <rangasai.v.chaganty@intel.com>