build: update minimum AIX OS level

Update minimum AIX OS level to 7.2 TL2. Looks like this
will be the version we can get into the CI so should be the
base level for 13.X and above and will be in support for the life
of 13.X.

PR-URL: #29476
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

BUILDING.md

@@ -116,7 +116,7 @@ platforms. This is true regardless of entries in the table below.
 | Windows          | arm64            | >= Windows 10                   | Experimental |                                   |
 | macOS            | x64              | >= 10.11                        | Tier 1       |                                   |
 | SmartOS          | x64              | >= 18                           | Tier 2       |                                   |
-| AIX              | ppc64be >=power7 | >= 7.1 TL05                     | Tier 2       |                                   |
+| AIX              | ppc64be >=power7 | >= 7.2 TL02                     | Tier 2       |                                   |
 | FreeBSD          | x64              | >= 11                           | Experimental | Downgraded as of Node.js 12       |
 
 <em id="fn1">1</em>: GCC 6 is not provided on the base platform, users will