ARM: dts: berlin: add 2nd clock for BG2Q sdhci0 and sdhci1

We removed CLK_IGNORE_UNUSED from CLKID_SDIO's flag, so the sdhci0 and
sdhci1 don't work. We fix this by adding the optional 2nd clock for
BG2Q's sdhci0 and sdhci1. This patch brings another benefit: the 2nd
clock can be disabled during runtime pm, so saves power a bit.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>