XTheadMae: Rename and cleanup memory attribute extension

We named the extension "MAEE" following the name of the enable bit
in the SxStatus CSR. However, the last 'E' stands for enable and should
therefore not be part of the name. Renaming an extension that has been
published is usually a no-go, but since we don't have any support
patches for "XTheadMaee" merged yet, we can get away with it.
Therefore, let's rename XTheadMaee to XTheadMae now.

Further cleanups:
* Streamline name to `XTheadMae`
* Simplify availability section (following other extensions)

Signed-off-by: Christoph Müllner <[email protected]>

xthead.adoc

@@ -52,4 +52,4 @@ include::xtheadvector.adoc[]
 
 include::intrinsic.adoc[]
 
-include::xtheadmaee.adoc[]
+include::xtheadmae.adoc[]

xtheadmae.adoc

@@ -0,0 +1,47 @@
+[#xtheadmae]
+== Memory Attribute Extension (XTheadMae)
+
+[NOTE,caption=Frozen]
+The `XTheadMae` extension is `stable`.
+
+Extension version: 1.0.
+
+The `XTheadMae` ISA extension provides a way to configure memory page attributes.
+These attributes are set in the page tabale entries (PTEs).
+
+The `XTheadMae` extension is a non-standard non-conforming extension.
+`XTheadMae` uses preserved [60:63] bits of the PTE, which have later been
+allocted to the `Svpbmt` and `Svnapot` standard extensions.
+This conflict is not on purpose, but the result of issues in the past that have been resolved since.
+Therefore, the `XTheadMae` extension and the `Svpbmt` or `Svnapot` are in conflict.
+In other words, tools should not allow to enable the `XTheadMae` extension and
+the `Svpbmt` or `Svnapot` extensions at the same time and should report an error
+if both are enabled by the user.
+
+The table below describes the page attributes corresponding to each memory type:
+
+[cols="^12,3,3,3",stripes=even,options="header"]
+|===
+| Memory type            | SO | C | B
+| Cacheable memory       | 0  | 1 | 1
+| Non-cacheable memory   | 0  | 0 | 1
+| Bufferable device      | 1  | 0 | 1
+| Non-bufferable device  | 1  | 0 | 0
+|===
+
+The table below describes extend page attributes in PTE:
+[cols="^3,^3,12",stripes=even,options="header"]
+|===
+| Fields  | Bit | Meaning
+| SO      | 63  | Strong order
+| C       | 62  | Cacheable
+| B       | 61  | Bufferable
+| T       | 60  | Trustable
+|===
+
+=== Availability
+
+The `XTheadMae` extension's availability can be probed via the
+`th.sxstatus`.MAEE bit (bit 21).
+The `XTheadMae` extension is available if and only if this bit is `1`.
+Refer to <<#xtheadsxstatus>> for more information about the `th.sxstatus` CSR.