cxl: Convert to ACQUIRE() for conditional rwsem locking

cxl: Convert to ACQUIRE() for conditional rwsem locking

Use ACQUIRE() to cleanup conditional locking paths in the CXL driver
The ACQUIRE() macro and its associated ACQUIRE_ERR() helpers, like
scoped_cond_guard(), arrange for scoped-based conditional locking. Unlike
scoped_cond_guard(), these macros arrange for an ERR_PTR() to be retrieved
representing the state of the conditional lock.

The goal of this conversion is to complete the removal of all explicit
unlock calls in the subsystem. I.e. the methods to acquire a lock are
solely via guard(), scoped_guard() (for limited cases), or ACQUIRE(). All
unlock is implicit / scope-based. In order to make sure all lock sites are
converted, the existing rwsem's are consolidated and renamed in 'struct
cxl_rwsem'. While that makes the patch noisier it gives a clean cut-off
between old-world (explicit unlock allowed), and new world (explicit unlock
deleted).

Cc: David Lechner <dlechner@baylibre.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Fabio M. De Francesco <fabio.m.de.francesco@linux.intel.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Shiju Jose <shiju.jose@huawei.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Fabio M. De Francesco <fabio.m.de.francesco@linux.intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Tested-by: Shiju Jose <shiju.jose@huawei.com>
Link: https://patch.msgid.link/20250711234932.671292-9-dan.j.williams@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>