Stop rpi-update deleting dt-blob.bin

dt-blob.bin is used to configure a platform's pin settings and clock settings and must not be changed when we do an rpi-update.  This is a function of the platform rather than a function of the operating system and therefore shouldn't be removed
Merge pull request #147 from ghollingworth/patch-1

Stop rpi-update deleting dt-blob.bin
Merge remote-tracking branch 'upstream/master'