fs: fat: extend for in-PBL support ...

The AT91 BootROM loads a boot.bin file from the first FAT partition
into SRAM, when booting from MMC. To avoid the need for two barebox
configurations for each of the bootloader stages, add PBL support
for reading from FAT. This way each stage need only have a different
PBL entry point.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

pbl: add block I/O API ...

We already have some PBL MCI implementations in barebox, but none
are used for chainloading a barebox from a file system.

There are some SoCs that would benefit from this however:
At least the Zynq, AT91, SoCFPGA and TI SoCs.

In preparation for supporting first stage boot on these where it's
customary for both the BootROM and first stage bootloader to load the
follow-up stage from FAT, add a very basic block I/O API that MCI
drivers can implement.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

include: add SPDX GPL-2.0-only license tags where applicable ...

Interpret "GPLv2" as "GPLv2 only".

Signed-off-by: Roland Hieber <rohieb@rohieb.name>
Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

pbl: Move piggy verification into pbl_barebox_uncompress() ...

piggy verification is a direct prerequisite of uncompressing the
piggydata, so move the verification there.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>

pbl: add sha256 and piggy verification to PBL ...

Extract the necessary functions from sha256 into a PBL headder and add a
verification function to the PBL. The function will be called before the
individual architectures decompress functions is run.

Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

pbl: Provide C macro to test if we are compiling the pbl ...

Provide IN_PBL as boolean constant which can be tested for in C.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

pbl: factorise decompressor ...

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>