locking/lockdep: Change 'static const' variables to enum values

gcc warns about 'static const' variables even in headers when building
with -Wunused-const-variables enabled:

In file included from kernel/locking/lockdep_proc.c:25:
kernel/locking/lockdep_internals.h:69:28: error: 'LOCKF_USED_IN_IRQ_READ' defined but not used [-Werror=unused-const-variable=]
   69 | static const unsigned long LOCKF_USED_IN_IRQ_READ =
      |                            ^~~~~~~~~~~~~~~~~~~~~~
kernel/locking/lockdep_internals.h:63:28: error: 'LOCKF_ENABLED_IRQ_READ' defined but not used [-Werror=unused-const-variable=]
   63 | static const unsigned long LOCKF_ENABLED_IRQ_READ =
      |                            ^~~~~~~~~~~~~~~~~~~~~~
kernel/locking/lockdep_internals.h:57:28: error: 'LOCKF_USED_IN_IRQ' defined but not used [-Werror=unused-const-variable=]
   57 | static const unsigned long LOCKF_USED_IN_IRQ =
      |                            ^~~~~~~~~~~~~~~~~
kernel/locking/lockdep_internals.h:51:28: error: 'LOCKF_ENABLED_IRQ' defined but not used [-Werror=unused-const-variable=]
   51 | static const unsigned long LOCKF_ENABLED_IRQ =
      |                            ^~~~~~~~~~~~~~~~~

This one is easy to avoid by changing the generated constant definition
into an equivalent enum.

Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20250409122314.2848028-6-arnd@kernel.org