CVE-2026-98469: KVM: arm64: Fix AArch32 DBGBXVR<n> handling

In the Linux kernel, the following vulnerability has been resolved:

KVM: arm64: Fix AArch32 DBGBXVR<n> handling

The consolidation of the breakpoint and watchpoint register accessors switched DBGBXVR<n> from trapbvr() to trapdbgwbreg(). The latter selects backing storage with demuxwbreg(), which only handles Op2 values 4 through 7. Since DBGBXVR<n> uses Op2 1, an AArch32 guest access hits KVMBUGON() and marks the VM dead.

DBGBXVR<n> aliases DBGBVR<n>EL1[63:32], and its AA32(HI) descriptor already selects the upper half. Map Op2 1 to dbgbvr[] alongside Op2 4, restoring the pre-regression behavior.