[Polly] Narrow IV to lower type when possible (#212708)

This patch tries to lower the LLVM-IR type of IVs which are set to i64
by default during polly codegen. This is specially beneficial for
Hexagon as it uses Hardware Loops which requires 32 bit wide IVs.

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Co-authored-by: Anilava Kundu <anilkund@hu-anilkund-blr.qualcomm.com>
Co-authored-by: Santanu Das <santdas@qti.qualcomm.com>
GitOrigin-RevId: 00cc5ac48769908583c25ae85f86b31b1696da6a