zephyr: Add Kconfig option CONFIG_BOOT_KEY_IMPORT_BYPASS_ASN

The option enables MCUboot configuration option
MCUBOOT_KEY_IMPORT_BYPASS_ASN.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>

boot/zephyr/Kconfig

@@ -183,6 +183,15 @@ config BOOT_ED25519_MBEDTLS
 	select BOOT_USE_MBEDTLS
 	select MBEDTLS
 endchoice
+
+config BOOT_KEY_IMPORT_BYPASS_ASN
+	bool "Directly access key value without ASN.1 parsing"
+	help
+	  Originally, public keys compiled into MCUboot were
+	  stored in ASN.1 encoded format. Enabling this option
+	  bypasses the ASN.1 decoding and directly accesses the key
+	  in ASN.1 bitstream; this reduces MCUboot code by removing
+	  the ASN.1 processing.
 endif
 
 endchoice