drivers: serial: simplify Kconfig.nrfx by using HAS_HW_NRF_UART0

Condition:
depends on ((SOC_SERIES_NRF52X || SOC_SERIES_NRF51X) && (!SOC_NRF52810))
for displaing configuration for UART0 peripheral has been replaced with:
depends on HAS_HW_NRF_UART0.

Signed-off-by: Jakub Rzeszutko <jakub.rzeszutko@nordicsemi.no>