boards: nrf5340dk_nrf5340_cpunet: Disable BT_ECC support

Disable BT_ECC support in network core to reduce RAM usage.
ECC implementation can instead be supported in the Host
running in the application core.

This is also to keep hci_uart (nRF52 Series) and hci_rpmsg
(nRF53 Series) have the same support features. ECC is not
enabled in hci_uart sample.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>
diff --git a/boards/arm/nrf5340dk_nrf5340/Kconfig.defconfig b/boards/arm/nrf5340dk_nrf5340/Kconfig.defconfig
index c5e1263..8a37801 100644
--- a/boards/arm/nrf5340dk_nrf5340/Kconfig.defconfig
+++ b/boards/arm/nrf5340dk_nrf5340/Kconfig.defconfig
@@ -135,12 +135,7 @@
 
 if BOARD_NRF5340DK_NRF5340_CPUNET
 
-# BT_CTLR depends on BT. When BT is enabled we should default to also
-# enabling the controller.
 config BT_CTLR
 	default y if BT
 
-config BT_ECC
-	default y if BT
-
 endif # BOARD_NRF5340DK_NRF5340_CPUNET
diff --git a/subsys/bluetooth/host/Kconfig b/subsys/bluetooth/host/Kconfig
index a30232f..0453747 100644
--- a/subsys/bluetooth/host/Kconfig
+++ b/subsys/bluetooth/host/Kconfig
@@ -43,6 +43,7 @@
 	# NOTE: This value is derived from other symbols and should only be
 	# changed if required by architecture
 	int "HCI ECC thread stack size"
+	depends on BT_TINYCRYPT_ECC
 	default 1140
 	help
 	  NOTE: This is an advanced setting and should not be changed unless