soc: qualcomm: Add Shared Memory Manager driver

The Shared Memory Manager driver implements an interface for allocating
and accessing items in the memory area shared among all of the
processors in a Qualcomm platform.

Adapted from the Linux driver (4.17)

Changes from the original Linux driver:
* Removed HW spinlock mechanism, which is irrelevant
in U-boot particualar use case, which is just reading from the smem.
* Adapted from Linux driver model to U-Boot's.

Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Ramon Fried <ramon.fried@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index 91e4ad7..a2293b7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -206,6 +206,7 @@
 M:	Ramon Fried <ramon.fried@gmail.com>
 S:	Maintained
 F:	arch/arm/mach-snapdragon/
+F:	drivers/smem/msm_smem.c
 
 ARM STI
 M:	Patrice Chotard <patrice.chotard@st.com>