ARM: efm32: switch to properly namespaced location property

Since commits:

281ec367 (i2c: efm32: correct namespacing of location property)
d36f47fa (serial: efm32: correct namespacing of location property)
10ed7e98 (spi: efm32: correct namespacing of location property)

(contained in 3.17-rc1) all drivers support the correctly
namespaced location property. So use the better names now.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>