bytes of boot2. Since we're in 16-bit mode, we can't copy all 128kB at
once; instead we loop four times and copy 32 kB each time.
This change was made necessary by an upcoming increase in the size of the
boot2 binary; should it increase further, the COPY_BLKS value can be
adjusted without anyone needing to remember 8086 assembly language again.
Requested by: allanjude
Tested by: allanjude
MFC after: 1 week
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