nanohub: add support for specifying a variant map file

add new linker script rule that accepts full path to map file
add NANO_VARIANT_LKR_MAP to specify a map file instead of the default
tell make not to delete os.checked.elf

Bug: 68819698
Test: Set NANO_VARIANT_LKR_MAP to a different map file and build
Change-Id: Ia2bd2cb3b9194ca41c6cd2ae98b0d724287fc18b
Signed-off-by: Ben Fennema <fennema@google.com>
3 files changed