[mlir][tosa][linalg] Apply direct tosa -> linalg Conv2D lowering

[FranklandJack]

TOSA defines the filter channel ordering for 2D convolution operation tosa.conv2d as [OC, KH, KW, IC]. The LinAlg dialect supports [F, H, W, C] and [H, W, C, F] orderings via the linalg.conv_2d_nhwc_fhwc and linalg.conv_2d_nhwc_hwcf operations respectively. Where F == OC, KH == H, KW == W and C == IC.

Currently tosa.conv2d is lowered to linalg.conv2d_nhwc_hwcf meaning we need to insert a transposition operation to permute the filter channels before they can be passed as weights to the linalg op, that is [F, H, W, C] -> [H, W, C, F]. An analogous transformation needs to be applied to the quantized operation that lowers to linalg.conv_2d_nhwc_hwcf_q.

This commit updates the TOSA->LinAlg lowering so that tosa.conv2d is lowered to linalg.conv2d_nhwc_fhwc removing the need for the introduction of a transposition operation and making the mapping 1-1. It also adds a linalg.conv_2d_nhwc_fhwc_q quantized operation to the LinAlg dialect so the same direct 1-1 mapping can be applied to the quantized variant.

This commit does not add any new lit tests but repurposes the current TosaToLinalgNamed tests by removing the checks for transpositions and updating the targeted LinAlg operations from linalg.conv2d_nhwc_hwcf to linalg.conv2d_nhwc_fhwc`.

[NatashaKnk]

Looks good, thanks!