configs: enable CONFIG_UNIT_TEST for all qemu* generic targets

configs: enable CONFIG_UNIT_TEST for all qemu* generic targets

The qemu* "generic" targets (i.e. not those emulating a particular
board) are typically used for testing as many features as possible,
especially in CI so it makes sense to have UNIT_TEST enabled for
all of the defconfigs for these targets.

Not enabling UNIT_TEST in qemu-x86_defconfig due to:

    LD      u-boot
  ld.bfd: section .rel.dyn VMA wraps around address space
  ld.bfd: section .start16 LMA [fffff800,fffff86f] overlaps section .rel.dyn LMA [ffffb77c,0002ac93]
  make: *** [Makefile:1824: u-boot] Error 1

Suggested-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>