[dv/mubi] Allow expressions for weights in `_DV_MUBI_DIST`
[dv/mubi] Allow expressions for weights in `_DV_MUBI_DIST`

The `T_WEIGHT_` and `F_WEIGHT_` arguments can be expressions.  Due to
operator precedence, the multiplication may apply only to the rightmost
term of such an expression, which is usually unintended.  Adding
parentheses around the weights prevents this.

Signed-off-by: Andreas Kurth <62c4a7f75976b7a2fb8d79afddaccc3e9236aad5@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan