We currently perform various min-entropy calculations using build-time
floating-point arithmetic.  No floating-point code ends up in the
final binary, since the results are eventually converted to integers
and asserted to be compile-time constants.

Though this mechanism is undoubtedly cute, it inhibits us from using
"-mno-sse" to prevent the use of SSE registers by the compiler.

Fix by using fixed-point arithmetic instead.

Signed-off-by: Michael Brown <mcb30@ipxe.org>