mb/amd/padmelon: rename to pademelon

This AMD reference board is called Pademelon and not Padmelon, so fix
the name in coreboot. Also update the corresponding documentation.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Id1c7331f5f3c34dc7ec4bc5a1f5fe3d12d503474
Reviewed-on: https://review.coreboot.org/c/coreboot/+/68426
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martin.roth@amd.corp-partner.google.com>

MAINTAINERS

@@ -153,7 +153,7 @@ L:	amd_coreboot_org_changes@googlegroups.com
 F:	src/mainboard/amd/gardenia/
 F:	src/mainboard/amd/inagua/
 F:	src/mainboard/amd/olivehill/
-F:	src/mainboard/amd/padmelon/
+F:	src/mainboard/amd/pademelon/
 F:	src/mainboard/amd/parmer/
 F:	src/mainboard/amd/persimmon/
 F:	src/mainboard/amd/south_station/