Update the ARM external toolchain to the latest 15.2.rel1 release from ARM. This involves: - Updating the version, site URL, and source filename in .mk - Updating the SHA256 hash in .hash - Updating the display name and GCC version dependency in Config.in Verified by booting on a default Qemu configuration. Signed-off-by: Dowan Gullient <dowan.gullient@smile.fr> Signed-off-by: Julien Olivain <ju.o@free.fr>