KVM: arm64: nvhe: Disable branch generation in nVHE guests

Disable the BRBE before we enter the guest, saving the status and enable it
back once we get out of the guest. This avoids capturing branch records in
the guest kernel or userspace, which would be confusing the host samples.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: James Morse <james.morse@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: kvmarm@lists.linux.dev
Cc: linux-arm-kernel@lists.infradead.org
CC: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
----
Changes in V17:

- Dropped isb() call sites in  __debug_[save|restore]_brbe()
- Changed to [read|write]_sysreg_el1() accessors in __debug_[save|restore]_brbe()

 arch/arm64/include/asm/kvm_host.h  |  5 ++++-
 arch/arm64/kvm/debug.c             |  5 +++++
 arch/arm64/kvm/hyp/nvhe/debug-sr.c | 31 ++++++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 1 deletion(-)