[nrf fromtree] drivers serial nrfx: Apply workaround also for bsim targets

Or more precisely, do not remove the workaround for them.
The current HW models are accurate enough in this area for the
workaround to work properly.

Signed-off-by: Alberto Escolar Piedras <[email protected]>
(cherry picked from commit fedda6d)

Author: aescolar

drivers/serial/uart_nrfx_uarte.c

@@ -30,9 +30,7 @@
 
 LOG_MODULE_REGISTER(uart_nrfx_uarte, CONFIG_UART_LOG_LEVEL);
 
-#if !defined(CONFIG_ARCH_POSIX)
 #define RX_FLUSH_WORKAROUND 1
-#endif
 
 #define UARTE(idx)                DT_NODELABEL(uart##idx)
 #define UARTE_HAS_PROP(idx, prop) DT_NODE_HAS_PROP(UARTE(idx), prop)