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 is just to avoid capturing records
in the guest kernel/userspace, which would be confusing the 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>