PR26610, ARM's "VFPv3 vldr to vmov" gas testcase fail

I removed a few too many parentheses in git commit 7af67752.  This
patch fixes that problem, rewriting the expression so it won't happen
again.  The patch also avoids more UB with shifts of signed values.

	PR 26610
	* config/tc-arm.c (move_or_literal_pool): Correct extraction of
	bignum.  Use unsigned "v"
	(is_double_a_single): Make "v" and "mantissa" unsigned.  Formatting.
	(double_to_single): Likewise.