warp7: io_storage: Add initial stub warp7_io_storage.c

This commit adds support for parsing a FIP pre-loaded by a previous
boot-phase such as u-boot or via ATF reading directly from eMMC.

[bod: squashing several patches from Rui, Jun and bod]

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Jun Nie <jun.nie@linaro.org>
Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>