The A64 ISA accepts distinct (but overlapping) ranges of immediates for:

 * add arithmetic instructions ('I' machine constraint)
 * sub arithmetic instructions ('J' machine constraint)
 * 32-bit logical instructions ('K' machine constraint)
 * 64-bit logical instructions ('L' machine constraint)

... but we currently use the 'I' constraint for many atomic operations
using sub or logical instructions, which is not always valid.

When CONFIG_ARM64_LSE_ATOMICS is not set, this allows invalid immediates
to be passed to instructions, potentially resulting in a build failure.
When CONFIG_ARM64_LSE_ATOMICS is selected the out-of-line ll/sc atomics
always use a register as they have no visibility of the value passed by
the caller.

This patch adds a constraint parameter to the ATOMIC_xx and
__CMPXCHG_CASE macros so that we can pass appropriate constraints for
each case, with uses updated accordingly.

Unfortunately prior to GCC 8.1.0 the 'K' constraint erroneously accepted
'4294967295', so we must instead force the use of a register.
Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>