device-libs: Use elementwise builtins for ldexp

[arsenm]

No description provided.

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[z1-cciauto]

PSDB Link: https://compiler-ci.amd.com/job/compiler-psdb-amd-staging/4054

[b-sumner]

Just checking...will this properly handle ldexp(vecN, int) as well as ldexp(vecN, intN) ?