kcsan: Introduce ASSERT_EXCLUSIVE_*() macros

Introduces ASSERT_EXCLUSIVE_WRITER() and ASSERT_EXCLUSIVE_ACCESS(), which
may be used to assert properties of synchronization logic, where
violation cannot be detected as a normal data race.

Examples of the reports that may be generated:

    ==================================================================
    BUG: KCSAN: assert: race in test_thread / test_thread

    write to 0xffffffffab3d1540 of 8 bytes by task 466 on cpu 2:
     test_thread+0x8d/0x111
     debugfs_write.cold+0x32/0x44
     ...

    assert no writes to 0xffffffffab3d1540 of 8 bytes by task 464 on cpu 0:
     test_thread+0xa3/0x111
     debugfs_write.cold+0x32/0x44
     ...
    ==================================================================

    ==================================================================
    BUG: KCSAN: assert: race in test_thread / test_thread

    assert no accesses to 0xffffffffab3d1540 of 8 bytes by task 465 on cpu 1:
     test_thread+0xb9/0x111
     debugfs_write.cold+0x32/0x44
     ...

    read to 0xffffffffab3d1540 of 8 bytes by task 464 on cpu 0:
     test_thread+0x77/0x111
     debugfs_write.cold+0x32/0x44
     ...
    ==================================================================

Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>