[rtl] Remove stall cycle with BT ALU
[rtl] Remove stall cycle with BT ALU

- Branches don't need to stall with the branch target ALU

Signed-off-by: Tom Roberts <f3b1a53ee1cbeb35a47033dea932030093853292@lowrisc.org>

lowRISC/ibex,lowRISC/ibex,AmbiML/ibex,lowRISC/ibex,AmbiML/ibex,AmbiML/ibex,lowRISC/ibex,AmbiML/ibex