pmc: clarify and strengthen statements about API/ABI

- Make it clear that applications are not only encouraged to use the
  pmc(3) library, but use of the hwpmc(4) interface directly is a
  use-case we do not support
- Move the COMPATIBILITY section above PROGRAMMING API in hwpmc(4)
- Drop statements about the driver and library being "under development"

Reviewed by:	jkoshy, emaste
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D40543

lib/libpmc/pmc.3

@@ -23,7 +23,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd April 5, 2023
+.Dd June 16, 2023
 .Dt PMC 3
 .Os
 .Sh NAME
@@ -542,11 +542,7 @@ In order to ease forward compatibility with future versions of the
 driver, applications are urged to dynamically link with the
 .Nm pmc
 library.
-.Pp
-The
-.Nm pmc
-API is
-.Ud
+Doing otherwise is unsupported.
 .Sh SEE ALSO
 .Xr pmc.atom 3 ,
 .Xr pmc.core 3 ,

share/man/man4/hwpmc.4

@@ -28,7 +28,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd May 31, 2023
+.Dd June 16, 2023
 .Dt HWPMC 4
 .Os
 .Sh NAME
@@ -281,14 +281,15 @@ Non-disabled hardware counters in such a row may be used
 for satisfying system scope allocation requests.
 No process scope PMCs will use hardware counters in this row.
 .El
-.Sh PROGRAMMING API
-The recommended way for application programs to use the facilities of
-the
-.Nm
-driver is using the API provided by the
+.Sh COMPATIBILITY
+The API and ABI documented in this manual page may change in the future.
+This interface is intended to be consumed by the
 .Xr pmc 3
-library.
-.Pp
+library; other consumers are unsupported.
+Applications targeting PMCs should use the
+.Xr pmc 3
+library API.
+.Sh PROGRAMMING API
 The
 .Nm
 driver operates using a system call number that is dynamically
@@ -519,16 +520,6 @@ The value for tunable
 .Va kern.hwpmc.nsamples
 was negative or greater than 65535.
 .El
-.Sh COMPATIBILITY
-The
-.Nm
-driver is
-.Ud
-The API and ABI documented in this manual page may change in
-the future.
-The recommended method of accessing this driver is using the
-.Xr pmc 3
-API.
 .Sh ERRORS
 A command issued to the
 .Nm