Draft: u-boot on emmc and /boot on sata

• u-boot-config: enable CONFIG_SATA_BOOT
• patches/0001-tweak-boot-commands.patch: also attempt booting from sata0
• build u-boot image for sd as well as for emmc
• switch to POSIX shell
• set -u
• make shellcheck clean
• avoid cd in favour of -C and env --chdir
• bump u-boot version from v2023.10-rc4 to v2023.10
• verify top git hashes for u-boot and atf
• verify that BPI Block Copy src is correct for sd and emmc
• verify that sd and emmc images differ only in the Block Copy src

marked as draft as we first have to test whether this works

patches/0001-tweak-boot-commands.patch

@@ -2,14 +2,12 @@ diff --git a/include/configs/ls1028a_common.h b/include/configs/ls1028a_common.h
 index 2ccb20192d..366739c834 100644
 --- a/include/configs/ls1028a_common.h
 +++ b/include/configs/ls1028a_common.h
-@@ -38,18 +38,20 @@
- #define BOOT_TARGET_DEVICES(func) \
+@@ -39,17 +39,19 @@
  	func(MMC, mmc, 0) \
  	func(MMC, mmc, 1) \
--	func(USB, usb, 0) \
+ 	func(USB, usb, 0) \
 -	func(DHCP, dhcp, na)
-+ 	func(USB, usb, 0)
-+
++	func(SATA, sata, 0)
  #include <config_distro_bootcmd.h>
  
 -#define XSPI_NOR_BOOTCOMMAND	\