gba: implement write protection for HALTCNT PR run #565

Job	Run time
Build ares (primary) / ares-windows-clang-cl-arm64	8m 45s
Build ares (primary) / ares-windows-x64	9m 5s
Build ares (primary) / ares-macos-universal	22m 55s
Build ares (auxiliary) / ares-windows-x64-gcc	19m 19s
Build ares (auxiliary) / ares-windows-msvc-arm64	9m 29s
Build ares (auxiliary) / ares-windows-arm64	7m 22s
Build ares (auxiliary) / ares-windows-clang-cl-x64	9m 4s
Build ares (auxiliary) / ares-windows-msvc-x64	7m 56s
Build ares (auxiliary) / ares-ubuntu-gcc-arm64	11m 35s
Build ares (auxiliary) / ares-freebsd	24m 53s
Build ares (auxiliary) / ares-ubuntu-clang-x64	16m 8s
Build ares (auxiliary) / ares-ubuntu-clang-arm64	11m 27s
Build ares (auxiliary) / ares-ubuntu-gcc-arm64-qt	11m 8s
Build ares (auxiliary) / ares-ubuntu-gcc-x64	15m 57s
	3h 5m 3s

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