main/postmarketos-mkinitfs: include crc32c_generic module by default (MR 3166)

CRC32C is required for ext4 to work, otherwise mounting the ext4 rootfs
fails with "Cannot load crc32c driver.".

main/postmarketos-mkinitfs/00-default.modules

 dm_crypt
 ext4
+crc32c_generic
 usb_f_rndis
 f2fs
 xts