base-files: upgrade: make get_partitions() endian agnostic

base-files: upgrade: make get_partitions() endian agnostic

This patch fixes two issues with the current get_partitions()
function.

First: "Invalid partition table on $disk" will pop up on
legitimate images on big endian system.

This is because the little-endian representation of "55 AA" is
assumed in the context of little-endian architectures. On these
comparing it to the 16-bit word 0xAA55 does work as intented.
Whereas on big-endian systems, this would have to be 0x55AA.

This patch fixes the issue by replacing the integer conversion
and value match check with just a string comparision.

Second: The extraction of the type, start LBA and LBA num from
the partition table has the same endianness issue. This has been
fixed by using the new hex_le32_to_cpu() function. This function
will translate the stored little-endian data to the correct
byte-order if necessary.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
(cherry picked from commit 4e3f6dae04fb526a78e613db6c65aee584403d36)