[SYCL][Doc] Specify usage of -fsyclbin and -fsycl-device-only together

[dm-vodopyanov]

The correct test is already there:

llvm/clang/test/Driver/fsyclbin.cpp

Lines 8 to 14 in 2532282

	/// -fsyclbin -fsycl-device-only usage. -fsycl-device-only will 'win' and
	/// -fsyclbin is effectively ignored.
	// RUN: %clangxx -fsycl-device-only -fsyclbin --offload-new-driver %s -### 2>&1 \
	// RUN: | FileCheck %s --check-prefix=SYCLBIN_UNUSED
	// RUN: %clang_cl -fsycl-device-only -fsyclbin --offload-new-driver %s -### 2>&1 \
	// RUN: | FileCheck %s --check-prefix=SYCLBIN_UNUSED
	// SYCLBIN_UNUSED: warning: argument unused during compilation: '-fsyclbin'