Move qualcomm.passes to qualcomm._passes (#5920)

Summary:
Changing qualcomm.passes to qualcomm._passes to indicate that these passes are not covered under the API stability guarantee.

Pull Request resolved: #5920

Reviewed By: helunwencser

Differential Revision: D63926845

fbshipit-source-id: f1e3187f3012f83b388d9635ca5a244fa36950d6

Author: tarun292

backends/qualcomm/README.md

@@ -46,7 +46,7 @@ backends/qualcomm
 |   └── python # Python interface for using QNN libraries.
 ├── builders # Codes for lowering each operators (AoT Part).
 ├── partition # QNN Partitioner (AoT Part).
-├── passes # Various passes helping lower models to QNN backend (AoT Part).
+├── _passes # Various private passes helping lower models to QNN backend (AoT Part).
 ├── python # Places to put pybind artifacts for accessing QNN APIs, structures, etc (AoT Part).
 ├── quantizer # QNN Quantizer
 ├── runtime # Here is QNN runtime responsbile for compiling a model on x64.

backends/qualcomm/TARGETS

@@ -13,6 +13,6 @@ runtime.python_library(
         "@EXECUTORCH_CLIENTS",
     ],
     deps = [
-        "//executorch/backends/qualcomm/passes:passes",
+        "//executorch/backends/qualcomm/_passes:passes",
     ],
 )