image-live.bbclass: support disable isohybrid for EFI-only boot

While NO PCBIOS and EFI only for ISO 9660 image, burn the image
to SandDisk USB stick, plug it into laptop, then boot laptop and
enter UEFI mode, there are two boot options in UEFI system.

Here is the steps:

$ echo 'MACHINE = "genericx86-64"' >> conf/local.conf
$ echo 'MACHINE_FEATURES:remove = "pcbios"' >> conf/local.conf
$ echo 'IMAGE_FSTYPES:pn-core-image-minimal = " live"' >> conf/local.conf
$ bitbake core-image-minimal
$ sudo dd if=tmp/deploy/images/genericx86-64/core-image-minimal-genericx86-64.rootfs.iso of=/dev/sda

Boot laptop and entery UEFI mode
...
Boot mode is set to: UEFI

UEFI BOOT:
    UEFI: SanDisk
    UEFI: SanDisk 2
...

In this case, PCBIOS is not used, calling isohybrid for ISO 9660 image
is not necessary, and do not call isohybrid for ISO 9660 image could
remove duplicated boot option in UEFI mode.

According to [1][2], use `[ "${PCBIOS}" != "1" ] && [ "${EFI}" = "1" ]' as the
EFI-only condition, the revert condition is `[ "${PCBIOS}" = "1" ] || [ "${EFI}" != "1" ]'

[1] https://git.openembedded.org/openembedded-core/commit/?id=be3fc8c07e84c654f55c5d09934dfbdc7ff7e2b6
[2] https://git.openembedded.org/openembedded-core/commit/?id=be95f54495bf9e03062f86b929c66cab6e385a03

(From OE-Core rev: 4ea24276ad3b6cf3d63a839f3c5fbe697ccd28cd)

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes-recipe/image-live.bbclass

@@ -147,7 +147,10 @@ build_iso() {
 		isohybrid_args="-u"
 	fi
 
-	isohybrid $isohybrid_args ${IMGDEPLOYDIR}/${IMAGE_NAME}.iso
+	# EFI only does not need isohybrid
+	if [ "${PCBIOS}" = "1" ]  || [ "${EFI}" != "1" ]; then
+		isohybrid $isohybrid_args ${IMGDEPLOYDIR}/${IMAGE_NAME}.iso
+	fi
 }
 
 build_fat_img() {