arm-trusted-firmware-mediatek: update to ATF 2.4 (2021-02-25)

arm-trusted-firmware-mediatek: update to ATF 2.4 (2021-02-25)

All necessary blobs are now contained in the upstream repository, no
more wild replacing of blobs needed.
This new version also contains new storage drivers for (SPI-)NAND which
already comes with support for FM35Q1GA, so that patch can be dropped
as well.
Tested on:
 * Bananapi BPi-R64
   - sdmmc-2ddr
   - emmc-2ddr
 * Linksys E8450
   - snand-1ddr

All works fine (booting Bananapi BPi-R64 from SD Card does NOT require
a signed image, so patch arm-trusted-firmware-mediatek to allow doing
that).

Signed-off-by: Daniel Golle <daniel@makrotopia.org>