zephyr: fix logging

The removal of CONFIG_BOOT_HAVE_LOGGING in 15aa6ef ("zephyr: remove
BOOT_HAVE_LOGGING Kconfig option") missed some uses. In particular,
the one in mcuboot_config.h that converts Kconfig options to MCUboot's
platform-agnostic configuration macros.

This broke logging even when the relevant Kconfig options were on.

Fix things up by using CONFIG_LOG instead.

Tested logging works again on nrf52840_pca10056. Build tested
nrf51_pca10056 to make sure it still fits. The nrf52840_pca10059 build
overflows flash by 0.16%, but that was a problem before 15aa6ef.

Signed-off-by: Marti Bolivar <marti.bolivar@nordicsemi.no>
diff --git a/boot/zephyr/boards/nrf51_pca10028.conf b/boot/zephyr/boards/nrf51_pca10028.conf
index 61b6568..bd4eaac 100644
--- a/boot/zephyr/boards/nrf51_pca10028.conf
+++ b/boot/zephyr/boards/nrf51_pca10028.conf
@@ -1,5 +1,6 @@
-# Due the small boot partition can't use logging and debug optimalization
-# out-off-the-box. For using these features need to increase boot partition via
-# zephyr DTS.
-CONFIG_BOOT_HAVE_LOGGING=n
+# Due the small boot partition, we can't enable logging or the debug
+# optimization level out off the box. You need to increase the boot
+# partition size with a zephyr DTS overlay to make MCUboot's debug
+# builds fit.
+CONFIG_LOG=n
 CONFIG_SIZE_OPTIMIZATIONS=y
diff --git a/boot/zephyr/boards/nrf52840_pca10059.conf b/boot/zephyr/boards/nrf52840_pca10059.conf
index fadde6a..8c59700 100644
--- a/boot/zephyr/boards/nrf52840_pca10059.conf
+++ b/boot/zephyr/boards/nrf52840_pca10059.conf
@@ -1,7 +1,7 @@
 # The UART is used for Serial Recovery, so logging requires
 # an RTT console, which is not available out of the box on this board.
 # Disable logging.
-CONFIG_BOOT_HAVE_LOGGING=n
+CONFIG_LOG=n
 
 # Serial
 CONFIG_SERIAL=y