Replace flash partitioning terminology

This change replaces the slot 0/1 terminology with primary/secondary
slot and replaces FLASH_AREA_IMAGE_0/1 with
FLASH_AREA_IMAGE_PRIMARY/SECONDARY. This naming convention may be more
understandable, fits better to MCUs with multiple images and it is an
architecture agnostic alternative as well.

Change-Id: I655a585f6ae023852c671ee6635399efe25209c9
Signed-off-by: David Vincze <david.vincze@arm.com>
Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/sim/mcuboot-sys/src/area.rs b/sim/mcuboot-sys/src/area.rs
index 8666aa1..9b13098 100644
--- a/sim/mcuboot-sys/src/area.rs
+++ b/sim/mcuboot-sys/src/area.rs
@@ -27,7 +27,7 @@
 
     /// Add a slot to the image.  The slot must align with erasable units in the flash device.
     /// Panics if the description is not valid.  There are also bootloader assumptions that the
-    /// slots are SLOT0, SLOT1, and SCRATCH in that order.
+    /// slots are PRIMARY_SLOT, SECONDARY_SLOT, and SCRATCH in that order.
     pub fn add_image(&mut self, base: usize, len: usize, id: FlashId, dev_id: u8) {
         let nid = id as usize;
         let orig_base = base;
@@ -196,4 +196,3 @@
     off: u32,
     size: u32,
 }
-