power_supply: Make goldfish_battery depend on GOLDFISH || COMPILE_TEST

Nearly all the other goldfish peripherals (mtd, keyboard, etc) have a
dependency on the main platform's GOLDFISH Kconfig item, but this one got
skipped.  Even with consistency as a justification, there was initial
resistance[1] from some people to adding it however, as they wanted the
extra compile coverage.

Now, with CONFIG_COMPILE_TEST, we have the middle ground that will give
people the coverage who want it, and let those who don't want it to skip
ever seeing the option presented.

[1] https://lkml.org/lkml/2013/2/27/333



Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>