hexagon: improve RMS_NORM and DIV accuracy (#21251)
* hexagon-rms_norm: fix RMS_NORM for non-aligned tensor sizes
Co-authored-by: Krishna Sridhar <srsr@qti.qualcomm.com>
* hexagon-div: perform DIV in fp16 domain for lower dsp archs
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Co-authored-by: Krishna Sridhar <srsr@qti.qualcomm.com>