hikey: Allow environment to store in eMMC and increase bootdelay

Current Hikey configuration allows us to store u-boot environment on uSD
card. But this will be useless if uSD card is not inserted, hence use
the onboard eMMC memory for storing environment at Boot1 partition.
While we are at it, let's increase the boot delay to 10s also.

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