vexpress64: move hardware setting from defconfig to Kconfig

The defconfigs for the Arm Juno board and the FVP model are quite large,
setting a lot of platform-fixed variables like SYS_TEXT_BASE.
As those values are not really a user choice, let's provide default
values for them in our Kconfig file, so a lot of cruft can be removed
from the defconfig files.
This also moves the driver selection out of there, since this is again
not something a user should really decide on. Instead we allow users to
enable or disable subsystems, and select the appropriate drivers based
on that in the Kconfig file.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 0691292..7e613c7 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1258,6 +1258,10 @@
 	select PL01X_SERIAL
 	select OF_CONTROL
 	select CLK
+	select BLK
+	select MTD_NOR_FLASH if MTD
+	select FLASH_CFI_DRIVER if MTD
+	select ENV_IS_IN_FLASH if MTD
 
 config TARGET_TOTAL_COMPUTE
 	bool "Support Total Compute Platform"