plat: marvell: armada: modify PLAT_FAMILY name for 37xx SoCs

The Marvell Armada 37xx SoCs-based platforms contain a bit
awkward directory structure because the currently only one
supported PLAT and PLAT_FAMILY are the same. Modify the latter
to 'a3k' in order to improve it and keep plat/marvell/armada
tree more consistent:

plat/marvell/
├── armada
│   ├── a3k
│   │   ├── a3700

[...]

│   ├── a8k
│   │   ├── a70x0

[...]

Change-Id: I693a6ef88e6ce49a326a3328875c90bbc186066a
Signed-off-by: Marcin Wojtas <mw@semihalf.com>

plat/marvell/armada/a3700/a3700/platform.mk → plat/marvell/armada/a3k/a3700/platform.mk

@@ -5,6 +5,6 @@
 # https://spdx.org/licenses
 #
 
-include plat/marvell/armada/a3700/common/a3700_common.mk
+include plat/marvell/armada/a3k/common/a3700_common.mk
 
 include plat/marvell/armada/common/marvell_common.mk

plat/marvell/armada/a3700/common/a3700_common.mk → plat/marvell/armada/a3k/common/a3700_common.mk

@@ -7,7 +7,7 @@
 
 MARVELL_PLAT_BASE		:= plat/marvell/armada
 MARVELL_PLAT_INCLUDE_BASE	:= include/plat/marvell/armada
-PLAT_FAMILY			:= a3700
+PLAT_FAMILY			:= a3k
 PLAT_FAMILY_BASE		:= $(MARVELL_PLAT_BASE)/$(PLAT_FAMILY)
 PLAT_INCLUDE_BASE		:= $(MARVELL_PLAT_INCLUDE_BASE)/$(PLAT_FAMILY)
 PLAT_COMMON_BASE		:= $(PLAT_FAMILY_BASE)/common