Disable LiteX serial IRQ support

The LiteX UART IRQ support / UART peripheral still exhibits
issues when IRQs are enabled.  These issues appear most
severe when deferred logging is enabled.

Temporarily disable IRQ support to restore functionality.

drivers/serial/Kconfig.litex

@@ -6,8 +6,10 @@
 config UART_LITEUART
 	bool "LiteUART serial driver"
 	depends on (SOC_RISCV32_LITEX_VEXRISCV || SOC_PPC64EL_LITEX_KESTREL)
-	select SERIAL_SUPPORT_INTERRUPT
+	# currently not supporting interrupts due to a bug in LiteUART Tx IRQ
+	depends on !SERIAL_SUPPORT_INTERRUPT
+	#select SERIAL_SUPPORT_INTERRUPT
 	select SERIAL_HAS_DRIVER
-	select UART_INTERRUPT_DRIVEN
+	#select UART_INTERRUPT_DRIVEN
 	help
 	  This option enables LiteUART serial driver.