[sw] Remove redundant dependency from sw_lib_uart build
[sw] Remove redundant dependency from sw_lib_uart build

UART driver should not be able to directly access any of the UART
peripheral defines.

Signed-off-by: Silvestrs Timofejevs <5a6466a3751cccdb6ee413d1e87698ed8baaba81@lowrisc.org>

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