mseal sysmap: add arch-support txt

Add Documentation/features/core/mseal_sys_mappings/arch-support.txt

N/A: the arch is 32bits only and mseal is not supported in 32 bits,
     therefore N/A (until mseal is available in 32 bits kernel).

[jeffxu@chromium.org: update to v3]
  Link: https://lkml.kernel.org/r/20250324151537.1106542-2-jeffxu@google.com
Link: https://lkml.kernel.org/r/20250321032627.4147562-2-jeffxu@google.com
Signed-off-by: Jeff Xu <jeffxu@chromium.org>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Eric Dumaze <edumazet@google.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: guoweikang <guoweikang.kernel@gmail.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Meghana Malladi <m-malladi@ti.com>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: peaktocreek

Documentation/features/core/mseal_sys_mappings/arch-support.txt

@@ -0,0 +1,30 @@
+#
+# Feature name:          mseal-system-mappings
+#         Kconfig:       ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
+#         description:   arch supports mseal system mappings
+#
+    -----------------------
+    |         arch |status|
+    -----------------------
+    |       alpha: | TODO |
+    |         arc: |  N/A |
+    |         arm: |  N/A |
+    |       arm64: |  ok  |
+    |        csky: |  N/A |
+    |     hexagon: |  N/A |
+    |   loongarch: | TODO |
+    |        m68k: |  N/A |
+    |  microblaze: |  N/A |
+    |        mips: | TODO |
+    |       nios2: |  N/A |
+    |    openrisc: |  N/A |
+    |      parisc: | TODO |
+    |     powerpc: | TODO |
+    |       riscv: | TODO |
+    |        s390: |  ok  |
+    |          sh: |  N/A |
+    |       sparc: | TODO |
+    |          um: | TODO |
+    |         x86: |  ok  |
+    |      xtensa: |  N/A |
+    -----------------------