[HIP] Fix HIP path detection

Fix two issues:

--hip-path should not do rigorous checking, i.e. if .hipVersion exists it
will use it, otherwise it will not error out but assumes the default
HIP version. This is to be consistent with --rocm-path behavior.

when HIP_PATH is empty, it should be ignored. This is to be consistent
with ROCM_PATH behavior.

Reviewed by: Artem Belevich

Differential Revision: https://reviews.llvm.org/D152734

Fixes: SWDEV-404771