Rename MAKE_FARPTR (and similar) to MAKE_FLATPTR.

The term "far pointer" is used in many 16bit specs, and it is
    different from what MAKE_FARPTR creates.  So, use the term "flat
    pointer" in the code to distinguish between the two meanings.
Also, use the suffix "_fl" consistently when working with "flat
    pointers".
diff --git a/src/post.c b/src/post.c
index c8e0669..6b42e34 100644
--- a/src/post.c
+++ b/src/post.c
@@ -72,12 +72,12 @@
 {
     dprintf(3, "init bda\n");
 
-    struct bios_data_area_s *bda = MAKE_FARPTR(SEG_BDA, 0);
+    struct bios_data_area_s *bda = MAKE_FLATPTR(SEG_BDA, 0);
     memset(bda, 0, sizeof(*bda));
 
     int esize = DIV_ROUND_UP(sizeof(struct extended_bios_data_area_s), 1024);
     SET_BDA(mem_size_kb, 640 - esize);
-    u16 eseg = FARPTR_TO_SEG((640 - esize) * 1024);
+    u16 eseg = FLATPTR_TO_SEG((640 - esize) * 1024);
     SET_BDA(ebda_seg, eseg);
 
     struct extended_bios_data_area_s *ebda = get_ebda_ptr();
@@ -122,7 +122,7 @@
 
     // Mark known areas as reserved.
     u16 ebda_seg = get_ebda_seg();
-    add_e820((u32)MAKE_FARPTR(ebda_seg, 0), GET_EBDA2(ebda_seg, size) * 1024
+    add_e820((u32)MAKE_FLATPTR(ebda_seg, 0), GET_EBDA2(ebda_seg, size) * 1024
              , E820_RESERVED);
     add_e820(BUILD_BIOS_ADDR, BUILD_BIOS_SIZE, E820_RESERVED);