arm64: dts: actions: Add uSD and eMMC support for Bubblegum96

Add uSD and eMMC support for Bubblegum96 board based on Actions Semi
S900 SoC. SD0 is connected to uSD slot and SD2 is connected to eMMC.
Since there is no PMIC support added yet, fixed regulator has been
used as a regulator node.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>