Remove PI from UR override fetch variables (#15191)

Cleaning up some remaining `PI` references found in the UR CMake fetch
file.

Renaming `SYCL_PI_UR_OVERRIDE_FETCH_CONTENT_REPO` and
`SYCL_PI_UR_OVERRIDE_FETCH_CONTENT_TAG` to
`SYCL_UR_OVERRIDE_FETCH_CONTENT_REPO` and
`SYCL_PI_UR_OVERRIDE_FETCH_CONTENT_TAG`.

Author: martygrant

sycl/cmake/modules/FetchUnifiedRuntime.cmake

@@ -11,9 +11,9 @@ endif()
 
 # Options to override the default behaviour of the FetchContent to include UR
 # source code.
-set(SYCL_PI_UR_OVERRIDE_FETCH_CONTENT_REPO
+set(SYCL_UR_OVERRIDE_FETCH_CONTENT_REPO
   "" CACHE STRING "Override the Unified Runtime FetchContent repository")
-set(SYCL_PI_UR_OVERRIDE_FETCH_CONTENT_TAG
+set(SYCL_UR_OVERRIDE_FETCH_CONTENT_TAG
   "" CACHE STRING "Override the Unified Runtime FetchContent tag")
 
 # Options to disable use of FetchContent to include Unified Runtime source code
@@ -160,11 +160,11 @@ if(SYCL_UR_USE_FETCH_CONTENT)
     ${UNIFIED_RUNTIME_TAG}
   )
 
-  if(SYCL_PI_UR_OVERRIDE_FETCH_CONTENT_REPO)
-    set(UNIFIED_RUNTIME_REPO "${SYCL_PI_UR_OVERRIDE_FETCH_CONTENT_REPO}")
+  if(SYCL_UR_OVERRIDE_FETCH_CONTENT_REPO)
+    set(UNIFIED_RUNTIME_REPO "${SYCL_UR_OVERRIDE_FETCH_CONTENT_REPO}")
   endif()
-  if(SYCL_PI_UR_OVERRIDE_FETCH_CONTENT_TAG)
-    set(UNIFIED_RUNTIME_TAG "${SYCL_PI_UR_OVERRIDE_FETCH_CONTENT_TAG}")
+  if(SYCL_UR_OVERRIDE_FETCH_CONTENT_TAG)
+    set(UNIFIED_RUNTIME_TAG "${SYCL_UR_OVERRIDE_FETCH_CONTENT_TAG}")
   endif()
 
   message(STATUS "Will fetch Unified Runtime from ${UNIFIED_RUNTIME_REPO}")

sycl/doc/GetStartedGuide.md

@@ -348,10 +348,10 @@ specific repository URL and revision tag used can be found in the file
 In order to enable developers, a number of CMake variables are available to
 control which revision of Unified Runtime should be used when building DPC++:
 
-* `SYCL_PI_UR_OVERRIDE_FETCH_CONTENT_REPO` is a variable which can be used to
+* `SYCL_UR_OVERRIDE_FETCH_CONTENT_REPO` is a variable which can be used to
   override the `UNIFIED_RUNTIME_REPO` variable used by `FetchContent` to attain
   the Unified Runtime source code.
-* `SYCL_PI_UR_OVERRIDE_FETCH_CONTENT_TAG` is a variable which can be used to
+* `SYCL_UR_OVERRIDE_FETCH_CONTENT_TAG` is a variable which can be used to
   override the `UNIFIED_RUNTIME_TAG` variable used by `FetchContent` to attain
   the Unified Runtime source code.
 * `SYCL_UR_USE_FETCH_CONTENT` is an option to control if CMake should use