[SYCL] Update LIT to support the latest BEs (intel#752)

 - add support for ext_intel_esimd_emulator BE. Only SYCL/ESIMD test
should be run for this BE;
 - switch to use actual BE names to avoid runtime warning;
 - updated documentation accordingly.

Author: vladimirlaz

SYCL/lit.cfg.py

@@ -328,11 +328,15 @@
         gpu_run_on_linux_substitute = "env SYCL_DEVICE_FILTER={SYCL_PLUGIN}:gpu,host ".format(SYCL_PLUGIN=config.sycl_be)
         gpu_check_on_linux_substitute = "| FileCheck %s"
 
+<<<<<<< HEAD
 <<<<<<< HEAD
     if config.sycl_be == "ext_oneapi_cuda":
 =======
     if config.sycl_be == "cuda":
 >>>>>>> 24faf9d67 ([SYCL][CUDA] Set PI_CUDA_ENABLE_IMAGE_SUPPORT before running Image tests (#702))
+=======
+    if config.sycl_be == "ext_oneapi_cuda":
+>>>>>>> 1349fce09 ([SYCL] Update LIT to support the latest BEs (#752))
         gpu_run_substitute += "SYCL_PI_CUDA_ENABLE_IMAGE_SUPPORT=1 "
 
 else: