lib: libubigen math compile error fix ...

A compile error appears in libubigen on PXA architecture, because of a
division of an long long by a int :
/home/rj/mio_linux/barebox/lib/libubigen.c:105: undefined reference to
`__aeabi_ldivmod' arm-linux-gnueabi-ld: BFD (GNU Binutils for Debian)
2.20.1.20100303 assertion fail ../../bfd/elf32-arm.c:12497

Fix it by using div_u64 instead.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

lib: add libubigen ...

Imported from mtd-utils and stripped down to needed functionality.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>