mem: Allow disabling of tXAW through a 0 activation limit
mem: Allow disabling of tXAW through a 0 activation limit

This patch fixes an issue where an activation limit of 0 was not
allowed. With this patch, setting the limit to 0 simply disables the
tXAW constraint.

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