Long long support is now unconditional in printf/scanf and related
helpers. Remove the Kconfig option, the conditional compilation in
libvsprintf/libvscanf/ultoa_invert, the build-time #error in the
rn2xx3 driver, and clean up CONFIG_LIBC_LONG_LONG entries from all
board defconfigs.
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>