Revert "kconfig: Update to CONFIG_FLOAT to CONFIG_FPU rename in zephyr"

This reverts commit b0890aeaa4433bb36bbb9c564736cfc88ffcfd33.

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 afe8c9b..8c24f54 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_FPU=n
+CONFIG_FLOAT=n
 
 # Boot
 CONFIG_BOOT_BANNER=n