Fix shift amount width in fma and fma_multi - bug triggered by fp8alt

Created by: lucabertaccini

Fix bug in fpnew_fma and fpnew_fma_multi triggered by the FP8ALT format. The SHIFT_AMOUNT_WIDTH parameter was not large enough to represent the maximum shift.

SHIFT_AMOUNT_WIDTH is used to define addend_shamt as logic [SHIFT_AMOUNT_WIDTH-1:0] addend_shamt;. The maximum value we need to represent with addend_shamt is 3 * PRECISION_BITS + 4. Therefore, we need to define SHIFT_AMOUNT_WIDTH = $clog2 (3 * PRECISION_BITS +5). ($clog2 (3 * PRECISION_BITS +4) would not be enough if 3 * PRECISION_BITS +4 is a power of two).