[SYCL][ROCm] Fix rocm_piPlatformsGet when there are no devices

[al42and]

hipGetDeviceCount returns the hipErrorNoDevice error when there are no
available devices. Instead of treating it as a PI error, we now properly
report that the platform is not available.

Before:

$ sycl-ls

PI HIP ERROR:
        Value:           100
        Name:            hipErrorNoDevice
        Description:     hipErrorNoDevice
        Function:        operator()
        Source Location: /nethome/aland/intel-sycl/llvm/sycl/plugins/rocm/pi_rocm.cpp:699

[opencl:0] GPU : Intel(R) OpenCL HD Graphics 3.0 [1.0.0]
[opencl:1] GPU : Intel(R) OpenCL HD Graphics 3.0 [1.0.0]
[level_zero:0] GPU : Intel(R) Level-Zero 1.1 [1.1.0]
[level_zero:1] GPU : Intel(R) Level-Zero 1.1 [1.1.0]
[host:0] HOST: SYCL host platform 1.2 [1.2]

After:

$ sycl-ls
[opencl:0] GPU : Intel(R) OpenCL HD Graphics 3.0 [1.0.0]
[opencl:1] GPU : Intel(R) OpenCL HD Graphics 3.0 [1.0.0]
[level_zero:0] GPU : Intel(R) Level-Zero 1.1 [1.1.0]
[level_zero:1] GPU : Intel(R) Level-Zero 1.1 [1.1.0]
[host:0] HOST: SYCL host platform 1.2 [1.2]

[smaslov-intel]

LGTM

[AerialMantis]

LGTM