arm: socfpga: gen5: fix ERR_PTR_OFFSET

The default implementation of ERR_PTR/PTR_ERR maps errno values at the
and of the address range (e.g. -EINVAL/-22 gets 0xFFFFFFEA).

For socfpga gen5 SPL, this doesn't really work, as the heap is nearly
at the end of the 32 bit address range.

This patch adjusts the ERR_PTR_OFFSET to map errno values into the range
of the Boot ROM, which should not be used for valid pointers.

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

arch/arm/mach-socfpga/Kconfig

@@ -1,5 +1,8 @@
 if ARCH_SOCFPGA
 
+config ERR_PTR_OFFSET
+	default 0xfffec000 if TARGET_SOCFPGA_GEN5 # Boot ROM range
+
 config NR_DRAM_BANKS
 	default 1