linux-postmarketos-mediatek-mt8173: upgrade to 6.15.3

Adam Thiederequested to merge
adamthiede/pmaports:mt8173-6153 into master

This release has some mediatek drm changes, hoping it fixes some problem with wlroots 0.19.

(did not fix the problem, but the kernel works the same as the previous one)

Edited by Adam Thiede

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