uboot-mxs: fix compile problems related to OpenSSL

uboot-mxs: fix compile problems related to OpenSSL

Use the UBOOT_MAKE_FLAGS defined in include/u-boot.mk and do not
overwrite them to compile the host tools against the shipped LibreSSL.
In addition add a patch to fix a compile problem when compiling the
tools against LibreSSL caused by differences in the API between OpenSSL
1.1 and LibreSSL.

This should fix the compile problems seen in build bot from time to time
by not depending on the host libssl-dev package any more but using the
LibreSSL version from OpenWrt.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>