e820: Rename memmap.c to e820map.c and use consistent "e820_" prefix

Rename memmap.c to e820map.c as the code in that file only deals with
maintaining the e820 map.  Move all the e820 definitions to new file
e820map.h and use a consistent "e820_" prefix on all exported
functions.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
diff --git a/Makefile b/Makefile
index 3a0d2e8..e5f28d4 100644
--- a/Makefile
+++ b/Makefile
@@ -36,7 +36,7 @@
     hw/blockcmd.c hw/floppy.c hw/ata.c hw/ramdisk.c \
     hw/lsi-scsi.c hw/esp-scsi.c hw/megasas.c
 SRC16=$(SRCBOTH)
-SRC32FLAT=$(SRCBOTH) post.c memmap.c malloc.c romfile.c x86.c optionroms.c \
+SRC32FLAT=$(SRCBOTH) post.c e820map.c malloc.c romfile.c x86.c optionroms.c \
     pmm.c font.c boot.c bootsplash.c jpeg.c bmp.c tcgbios.c sha1.c \
     hw/ahci.c hw/pvscsi.c hw/usb-xhci.c hw/usb-hub.c hw/sdcard.c \
     fw/coreboot.c fw/lzmadecode.c fw/multiboot.c fw/csm.c fw/biostables.c \