Fix detection of qcdt boot images

mkbootimg from osm0sis changed the filename of the dtb section in [1] which breaks the detection of qcdt in pmbootstrap.

Fix this by adjusting the filename pmbootstrap checks to match the unpackbootimg behavior.

[1] https://github.com/osm0sis/mkbootimg/commit/d8222a4d

---

Quote from the commit:

add workarounds for new dtb section, rename old pre-version dt_size dtb to dt to differentiate

So I'm not 100% sure this is the correct fix for all devices but it works fine for the test image.

For reference the files produced by the old mkbootimg version we had packaged (commit cbc8c8260ea9f670857678d689c1d56778935522):

-rw-r--r-- 1 luca luca   9 Okt 14 22:45 qcdt-boot.img-base
-rw-r--r-- 1 luca luca   1 Okt 14 22:45 qcdt-boot.img-board
-rw-r--r-- 1 luca luca  23 Okt 14 22:45 qcdt-boot.img-cmdline
-rw-r--r-- 1 luca luca  10 Okt 14 22:45 qcdt-boot.img-dtb
-rw-r--r-- 1 luca luca   5 Okt 14 22:45 qcdt-boot.img-hash
-rw-r--r-- 1 luca luca   9 Okt 14 22:45 qcdt-boot.img-kerneloff
-rw-r--r-- 1 luca luca   5 Okt 14 22:45 qcdt-boot.img-pagesize
-rw-r--r-- 1 luca luca   0 Okt 14 22:45 qcdt-boot.img-ramdisk.gz
-rw-r--r-- 1 luca luca   9 Okt 14 22:45 qcdt-boot.img-ramdiskoff
-rw-r--r-- 1 luca luca   9 Okt 14 22:45 qcdt-boot.img-secondoff
-rw-r--r-- 1 luca luca   9 Okt 14 22:45 qcdt-boot.img-tagsoff
-rw-r--r-- 1 luca luca   0 Okt 14 22:45 qcdt-boot.img-zImage

And the new version (commit e2e244d95811473be39c8b0676193f49b7b4310e):

-rw-r--r-- 1 luca luca   9 Okt 14 22:46 qcdt-boot.img-base
-rw-r--r-- 1 luca luca   1 Okt 14 22:46 qcdt-boot.img-board
-rw-r--r-- 1 luca luca  23 Okt 14 22:46 qcdt-boot.img-cmdline
-rw-r--r-- 1 luca luca  10 Okt 14 22:46 qcdt-boot.img-dt
-rw-r--r-- 1 luca luca   5 Okt 14 22:46 qcdt-boot.img-hash
-rw-r--r-- 1 luca luca   9 Okt 14 22:46 qcdt-boot.img-kerneloff
-rw-r--r-- 1 luca luca   5 Okt 14 22:46 qcdt-boot.img-pagesize
-rw-r--r-- 1 luca luca   0 Okt 14 22:46 qcdt-boot.img-ramdisk.gz
-rw-r--r-- 1 luca luca   9 Okt 14 22:46 qcdt-boot.img-ramdiskoff
-rw-r--r-- 1 luca luca   9 Okt 14 22:46 qcdt-boot.img-secondoff
-rw-r--r-- 1 luca luca   9 Okt 14 22:46 qcdt-boot.img-tagsoff
-rw-r--r-- 1 luca luca   0 Okt 14 22:46 qcdt-boot.img-zImage