arm64: Convert pte handling from inline asm to using (cmp)xchg

arm64: Convert pte handling from inline asm to using (cmp)xchg

With the support for hardware updates of the access and dirty states,
the following pte handling functions had to be implemented using
exclusives: __ptep_test_and_clear_young(), ptep_get_and_clear(),
ptep_set_wrprotect() and ptep_set_access_flags(). To take advantage of
the LSE atomic instructions and also make the code cleaner, convert
these pte functions to use the more generic cmpxchg()/xchg().

Reviewed-by: Will Deacon <will.deacon@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit 3bbf7157ac66a88d94b291d4d5e2b2a9319a0f90)

CVE-2017-5753
CVE-2017-5715
CVE-2017-5754

Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>