SIZE_MAX was mistakenly redefined from UINT32_MAX to UINT64_MAX
on AArch32 when the arch-specific headers were merged.

This value is not currently used by upstream TF-A source code,
so no functionality should be affected.

Change-Id: I2acf7f8736423697c7377e8ed4b08843ced26e66
Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>