kconfig: Update to CONFIG_FLOAT to CONFIG_FPU rename in zephyr

Update CONFIG_FLOAT to CONFIG_FPU which has been renamed in zephyr.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>
Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
diff --git a/boot/zephyr/boards/nrf52_minimal_footprint.conf b/boot/zephyr/boards/nrf52_minimal_footprint.conf
index 8c24f54..afe8c9b 100644
--- a/boot/zephyr/boards/nrf52_minimal_footprint.conf
+++ b/boot/zephyr/boards/nrf52_minimal_footprint.conf
@@ -53,7 +53,7 @@
 # Memory protection
 CONFIG_MEMORY_PROTECTION=n
 CONFIG_THREAD_CUSTOM_DATA=n
-CONFIG_FLOAT=n
+CONFIG_FPU=n
 
 # Boot
 CONFIG_BOOT_BANNER=n