Some USB devices cause the USB stack to get stuck with a stall error.
This adds a patch which recovers from this situation.
This avoids an U-Boot crash when Arduino Mega R3 devices are connected,
which cause an USB stall when trying to read the product string.
When a USB keyboard is connected to Raspberry Pi 32-bit versions of
U-Boot crashed in certain situations just before booting Linux. This
seems to be cause by a buffer overflow when removing the USB keyboard
before hand-over to Linux.
Since 0001-CMD-read-string-from-fileinto-env.patch is in the global
directory to be applied for U-Boot, drop it from the Raspberry Pi
specific patch directory.
Bump to the latest U-Boot release 2021.04-rc4. This alows to drop quite
some patches which have been sent to the mailing list or picked from the
mailing list and have been merged upstream now.
