arm64: entry: Allow handling of undefined instructions from EL1

arm64: entry: Allow handling of undefined instructions from EL1

BugLink: https://bugs.launchpad.net/bugs/1836802
[ Upstream commit 0bf0f444b2c49241b2b39aa3cf210d7c95ef6c34 ]

Rather than panic() when taking an undefined instruction exception from
EL1, allow a hook to be registered in case we want to emulate the
instruction, like we will for the SSBS PSTATE manipulation instructions.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>