x86: fix debug trace output for mwait
x86: fix debug trace output for mwait

When running with the Exec flag, the mwait instruction attempted
to print out its source registers, which were never actually
initialized. This led to sporadic assertion failures when the
value stored there was invalid.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>

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