linux-postmarketos-qcom-sm6125: upgrade to 6.0

This MR bumps the version and ref for linux-postmarketos-qcom-sm6125. I've taken the chance to also fix an issue presented previously in the kernel fork, in which I accidentally set CONFIG_PHY_QCOM_QUSB2 to M instead of Y, making it not probe the USB port from boot, but instead from postmarketOS, which presents an issue when netbooting or wanting to use the debug shell.