boards: ambiq: apollo4p_blue_kxr_evb: update Bluetooth configuration

There is new added build_assert in the Bluetooth host stack to require
CONFIG_BT_BUF_EVT_RX_COUNT larger than CONFIG_BT_BUF_ACL_TX_COUNT.
Update the specific Bluetooth configurations to fix the build assert of
Bluetooth samples.

Signed-off-by: Aaron Ye <[email protected]>

Author: aaronyegx

boards/ambiq/apollo4p_blue_kxr_evb/Kconfig.defconfig

@@ -19,6 +19,9 @@ config MAIN_STACK_SIZE
 config BT_BUF_ACL_TX_COUNT
 	default 14
 
+config BT_BUF_EVT_RX_COUNT
+	default 15
+
 config BT_BUF_CMD_TX_SIZE
 	default $(UINT8_MAX)