vexpress64: Kconfig: move board definitions out of arch/arm

At the moment we define three "VExpress64" boards in arch/arm/Kconfig,
plus have a second Kconfig file in board/armltd/Kconfig.
One of those three boards is actually bogus (TARGET_VEXPRESS64_AEMV8A),
that stanza looks like being forgotten in a previous cleanup.

To remove the clutter from the generic Kconfig file, just define some
ARCH_VEXPRESS64 symbol there, enable some common options, and do the
board/model specific configuration in the board/armltd Kconfig file.

That allows to streamline and fine tune the configuration later, and
to also pull a lot of "non user choices" out of the defconfigs.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index b5ca14f..8f70d5d 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1250,34 +1250,12 @@
 	imply DISTRO_DEFAULTS
 	imply FAT_WRITE
 
-config TARGET_VEXPRESS64_AEMV8A
-	bool "Support vexpress_aemv8a"
+config ARCH_VEXPRESS64
+	bool "Support ARMv8 Arm Ltd. VExpress based boards and models"
 	select ARM64
-	select GPIO_EXTRA_HEADER
-	select PL01X_SERIAL
-
-config TARGET_VEXPRESS64_BASE_FVP
-	bool "Support Versatile Express ARMv8a FVP BASE model"
-	select ARM64
-	select GPIO_EXTRA_HEADER
-	select PL01X_SERIAL
-	select SEMIHOSTING
-
-config TARGET_VEXPRESS64_JUNO
-	bool "Support Versatile Express Juno Development Platform"
-	select ARM64
-	select GPIO_EXTRA_HEADER
-	select PL01X_SERIAL
 	select DM
-	select OF_CONTROL
-	select CLK
 	select DM_SERIAL
-	select ARM_PSCI_FW
-	select PSCI_RESET
-	select DM_ETH
-	select BLK
-	select USB
-	imply OF_HAS_PRIOR_STAGE
+	select PL01X_SERIAL
 
 config TARGET_TOTAL_COMPUTE
 	bool "Support Total Compute Platform"