mobicore: create readme for mobicore driver.

Create readme file for mobicore driver.
MobiCore is an operating system being shipped with TZBSP
on msm chipsets. MobiCore consists of several components in
the secure world(TrustZone) and non-secure world(linux
kernel, Android user space). The MobiCore driver
communicates with the MobiCore kernel that exists in
TrustZone.

Signed-off-by: Lukas Hänel <lukas.haenel@gi-de.com>
(cherry picked from commit 70c408cacd0722652f1eb85492314ada68801333)
Change-Id: I008b973706091c10db9c785f1b1758022eb3e8b9
Signed-off-by: Ramesh Masavarapu <rameshm@codeaurora.org>

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>