x86: Allow atomic MM_CONTEXT flags setting

So far there's no need in atomic setting of MM context flags in
mm_context_t::flags. The flags set early in exec and never change
after that.

LAM enabling requires atomic flag setting. The upcoming flag
MM_CONTEXT_FORCE_TAGGED_SVA can be set much later in the process
lifetime where multiple threads exist.

Convert the field to unsigned long and do MM_CONTEXT_* accesses with
__set_bit() and test_bit().

No functional changes.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Alexander Potapenko <glider@google.com>
Link: https://lore.kernel.org/all/20230312112612.31869-3-kirill.shutemov%40linux.intel.com