regulator: Fix mc13xxx regulator modular build (again)

Since mc13xxx-regulator-core.c and the actual drivers can get built
into seperate modules, you have to export the DT support symbols
"mc13xxx_get_num_regulators_dt" and "mc13xxx_parse_regulators_dt"
otherwise the allmodconfig build fails on sparc64.

[Updated the subject; the same thing was previously reported and fixed
in -next but for some reason nobody noticed for some considerable time
after the issue was introduced -- broonie]

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>