imx7: imx_regs: Add a shared imx-regs.h for i.MX7 ATF platforms

imx7: imx_regs: Add a shared imx-regs.h for i.MX7 ATF platforms

In order to have some common code shared between similar SOCs its pretty
common to have IP blocks reused. In reusing those blocks we frequently need
to map compatible blocks to different addresses depending on the SOC.

This patch adds a basic memory map of the i.MX7 based on the "Cortex-A7
Memory Map" section 2.12 of "i.MX7Solo Applications Processor Reference
Manual, Rev 0.1 08/2016"

In memory map terms the i.MX7S and i.MX7D are identical with the D
variant containing two Cortex-A7 cores plus a Cortex-M core and the S
variant containing one Cortex-A7 and one Cortex-M.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>