arm64: kernel: Save and restore UAO and addr_limit on exception entry

arm64: kernel: Save and restore UAO and addr_limit on exception entry

If we take an exception while at EL1, the exception handler inherits
the original context's addr_limit and PSTATE.UAO values. To be consistent
always reset addr_limit and PSTATE.UAO on (re-)entry to EL1. This
prevents accidental re-use of the original context's addr_limit.

Based on a similar patch for arm from Russell King.

Cc: <[email protected]> # 4.6-
Acked-by: Will Deacon <[email protected]>
Reviewed-by: Mark Rutland <[email protected]>
Signed-off-by: James Morse <[email protected]>
Signed-off-by: Will Deacon <[email protected]>