[quant] torch.mean add path for unsupported QNNPACK modes (#45533)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/45533
Test Plan: Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D24030446
Pulled By: z-a-f
fbshipit-source-id: a392402ef701c5e45e244ac440bc151ef942cccd
