Kconfig add config ERR_PTR_OFFSET

Kconfig add config ERR_PTR_OFFSET

Some U-Boot pointers have redundant information, so we can use a scheme
where we can return either an error code or a pointer with the same
return value. The default implementation just casts the pointer to a
number, however, this may fail on platforms where the end of the address
range is used for valid pointers (e.g. 0xffffff00 is a valid heap pointer
in socfpga SPL). For such platforms, this value provides an upper range
of those error pointer values - up to 'MAX_ERRNO' bytes below this value
must be unused/invalid addresses.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>