ci: drop dead VK_CPU option

Unused since 1eca809680 ("ci/v3dv: test v3dv in arm64
environment"), and in the meantime other code paths have been added and
do not support this (`.gitlab-ci/common/init-stage2.sh` when starting
xorg & wayland for instance), so instead of fixing dead code, let's
remove it.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29201>

.gitlab-ci/common/generate-env.sh

@@ -119,7 +119,6 @@ VARS=(
     VIRGL_HOST_API
     VIRGL_RENDER_SERVER
     WAFFLE_PLATFORM
-    VK_CPU
     VK_DRIVER
     # required by virglrender CI
     VK_DRIVER_FILES

.gitlab-ci/deqp-runner.sh

@@ -18,7 +18,8 @@ INSTALL=$(realpath -s "$PWD"/install)
 # Set up the driver environment.
 export LD_LIBRARY_PATH="$INSTALL"/lib/:$LD_LIBRARY_PATH
 export EGL_PLATFORM=surfaceless
-export VK_DRIVER_FILES="$PWD"/install/share/vulkan/icd.d/"$VK_DRIVER"_icd.${VK_CPU:-$(uname -m)}.json
+ARCH=$(uname -m)
+export VK_DRIVER_FILES="$PWD"/install/share/vulkan/icd.d/"$VK_DRIVER"_icd."$ARCH".json
 export OCL_ICD_VENDORS="$PWD"/install/etc/OpenCL/vendors/
 
 if [ -n "$USE_ANGLE" ]; then

.gitlab-ci/piglit/piglit-runner.sh

@@ -13,7 +13,8 @@ INSTALL="$PWD/install"
 # Set up the driver environment.
 export LD_LIBRARY_PATH="$INSTALL/lib/"
 export EGL_PLATFORM=surfaceless
-export VK_DRIVER_FILES="$INSTALL/share/vulkan/icd.d/${VK_DRIVER}_icd.${VK_CPU:-$(uname -m)}.json"
+ARCH=$(uname -m)
+export VK_DRIVER_FILES="$INSTALL/share/vulkan/icd.d/${VK_DRIVER}_icd.$ARCH.json"
 
 RESULTS=$PWD/${PIGLIT_RESULTS_DIR:-results}
 mkdir -p $RESULTS

.gitlab-ci/piglit/piglit-traces.sh

@@ -54,7 +54,8 @@ if [ -n "${VK_DRIVER}" ]; then
   export DXVK_LOG="$RESULTS/dxvk"
   [ -d "$DXVK_LOG" ] || mkdir -pv "$DXVK_LOG"
   export DXVK_STATE_CACHE=0
-  export VK_DRIVER_FILES="$INSTALL/share/vulkan/icd.d/${VK_DRIVER}_icd.${VK_CPU:-$(uname -m)}.json"
+  ARCH=$(uname -m)
+  export VK_DRIVER_FILES="$INSTALL/share/vulkan/icd.d/${VK_DRIVER}_icd.$ARCH.json"
 fi
 
 # Sanity check to ensure that our environment is sufficient to make our tests