[doc][ext] Update HIP/L0 support in p2p doc (#15847)

The extension document was out of date since it stated that P2P access
only worked on CUDA. This updates it to clarify that P2P access is also
supported on hip and l0 backends.

Signed-off-by: JackAKirk <[email protected]>

Author: JackAKirk

sycl/doc/extensions/supported/sycl_ext_oneapi_peer_access.asciidoc

@@ -36,7 +36,7 @@ https://github.com/intel/llvm/issues
 
 == Dependencies
 
-This extension is written against the SYCL 2020 revision 7 specification.  All
+This extension is written against the SYCL 2020 revision 9 specification.  All
 references below to the "core SYCL specification" or to section numbers in the
 SYCL specification refer to that revision.
 
@@ -47,8 +47,10 @@ This extension is implemented and fully supported by DPC++.
 == Backend support status
 
 This extension is currently implemented in DPC++ for all GPU devices and
-backends, however, only the CUDA backend allows peer to peer memory access.
-Other backends report false from the `ext_oneapi_can_access_peer` query.
+backends; however, only the CUDA, HIP and Level Zero backends allows peer to
+peer memory access. Other backends report false from the
+`ext_oneapi_can_access_peer` query. Peer-Peer memory access is only possible
+between two devices from the same backend.
 
 == Overview