[tosa] Legalize tfl.rfft2d to tosa.rfft2d
Since #59606 was merged, this is ready for review :) cc @rsuderman @jpienaar (I don't know why AMD build failed here) friendly ping if you have some free time :) - the AMD build failure doesn't look related
In the case the provided fft_length > the input height or width, a tfl.pad operation is automatically inserted. When fft_length < the input height or width, a slice is manually inserted to crop the input.

~Note: this PR relies on commits from #59606 and therefore also contains the contents of #59606.~

Signed-off-by: Luke Hutton <luke.hutton@arm.com>