zephyr: Add processing of PERUSER mgmt group for serial recovery

The commit adds Zephyr specific function for processing commands
from PERUSER and above groups; current addition is command
that allows to erase storage partition.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>
diff --git a/boot/zephyr/Kconfig b/boot/zephyr/Kconfig
index 8ef5345..0c11519 100644
--- a/boot/zephyr/Kconfig
+++ b/boot/zephyr/Kconfig
@@ -553,7 +553,7 @@
 	  serial recovery.
 
 config ENABLE_MGMT_PERUSER
-	bool "Enables system specific mcumgr commands"
+	bool "Enable system specific mcumgr commands"
 	depends on BOOT_SERIAL_UART
 	help
 	  The option enables processing of system specific mcumgr commands;