sim: Add support for serializing BitUnionXX
sim: Add support for serializing BitUnionXX

BitUnion instances can normally not be used with the SERIALIZE_SCALAR
and UNSERIALIZE_SCALAR macros due to the way they are converted
between their storage type and their actual type. This changeset adds
a set of parm(In|Out) functions specifically for gem5 bit unions to
work around the issue.

sobercoder/gem5,cancro7/gem5,kaiyuanl/gem5,sobercoder/gem5,powerjg/gem5-ci-test,Weil0ng/gem5,gedare/gem5,TUD-OS/gem5-dtu,gem5/gem5,briancoutinho0905/2dsampling,aclifton/cpeg853-gem5,cancro7/gem5,cancro7/gem5,rjschof/gem5,austinharris/gem5-riscv,rallylee/gem5,Weil0ng/gem5,markoshorro/gem5,rallylee/gem5,sobercoder/gem5,sobercoder/gem5,KuroeKurose/gem5,TUD-OS/gem5-dtu,rallylee/gem5,Weil0ng/gem5,gedare/gem5,HwisooSo/gemV-update,kaiyuanl/gem5,rallylee/gem5,cancro7/gem5,powerjg/gem5-ci-test,SanchayanMaity/gem5,briancoutinho0905/2dsampling,austinharris/gem5-riscv,TUD-OS/gem5-dtu,gem5/gem5,sobercoder/gem5,KuroeKurose/gem5,briancoutinho0905/2dsampling,qizenguf/MLC-STT,rjschof/gem5,rallylee/gem5,zlfben/gem5,gedare/gem5,austinharris/gem5-riscv,markoshorro/gem5,markoshorro/gem5,KuroeKurose/gem5,SanchayanMaity/gem5,qizenguf/MLC-STT,zlfben/gem5,zlfben/gem5,qizenguf/MLC-STT,rallylee/gem5,HwisooSo/gemV-update,powerjg/gem5-ci-test,KuroeKurose/gem5,SanchayanMaity/gem5,kaiyuanl/gem5,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,gedare/gem5,powerjg/gem5-ci-test,rjschof/gem5,SanchayanMaity/gem5,gem5/gem5,gedare/gem5,markoshorro/gem5,cancro7/gem5,sobercoder/gem5,Weil0ng/gem5,rjschof/gem5,SanchayanMaity/gem5,aclifton/cpeg853-gem5,zlfben/gem5,HwisooSo/gemV-update,KuroeKurose/gem5,aclifton/cpeg853-gem5,austinharris/gem5-riscv,Weil0ng/gem5,rjschof/gem5,qizenguf/MLC-STT,gem5/gem5,markoshorro/gem5,powerjg/gem5-ci-test,briancoutinho0905/2dsampling,KuroeKurose/gem5,cancro7/gem5,powerjg/gem5-ci-test,qizenguf/MLC-STT,gem5/gem5,gedare/gem5,austinharris/gem5-riscv,gedare/gem5,Weil0ng/gem5,briancoutinho0905/2dsampling,austinharris/gem5-riscv,TUD-OS/gem5-dtu,HwisooSo/gemV-update,KuroeKurose/gem5,sobercoder/gem5,kaiyuanl/gem5,rjschof/gem5,markoshorro/gem5,aclifton/cpeg853-gem5,HwisooSo/gemV-update,briancoutinho0905/2dsampling,zlfben/gem5,gem5/gem5,aclifton/cpeg853-gem5,qizenguf/MLC-STT,zlfben/gem5,HwisooSo/gemV-update,briancoutinho0905/2dsampling,TUD-OS/gem5-dtu,HwisooSo/gemV-update,aclifton/cpeg853-gem5,kaiyuanl/gem5,rjschof/gem5,rallylee/gem5,markoshorro/gem5,aclifton/cpeg853-gem5,SanchayanMaity/gem5,cancro7/gem5,qizenguf/MLC-STT,kaiyuanl/gem5,SanchayanMaity/gem5,kaiyuanl/gem5,gem5/gem5,powerjg/gem5-ci-test,zlfben/gem5,austinharris/gem5-riscv,Weil0ng/gem5