create DRAM_BASE_ADDRESS and SIZE config parameters

[zephyrbot]

Reported by Chuck Jordan:

Some boards do not have SRAM. They have DRAM.
There may be some boards in the future that have both SRAM and DRAM.

So probably, for all targets, there should be
CONFIG_DRAM_BASE_ADDRESS
CONFIG_DRAM_SIZE
configurable parameters.

Those boards that don't sport DRAM could set the size to 0 or something.

There is the further problem that some tests and samples are using
CONFIG_SRAM*, but this is not going to work in all situations.
The memory map can be quite complex with code in some memories, and various data
objects in various other memories.
So having a test or a sample that works on all targets might be a bit tricky, unless with
pollute them with board-specific conditional compilation.

This is a GENERAL problem that needs to be solved.
My specific need is that em_starterkit, for example, doesn't have SRAM but does have DRAM. It is confusing to be using the SRAM_BASE/SIZE configuration for DRAM.

(Imported from Jira ZEP-1151)

[zephyrbot]

by Sharron LIU:

This also looks like missing feature. Probably convert to a story?

[zephyrbot]

by Mark Linkmeyer:

Fixing incorrect priority

[nashif]

obsoleted with DTS introduction.