Add uart2 test program

Reads input from uart and then writes it back out again immediately.

hw/efinix_fpga/test_programs/uart2.s

@@ -0,0 +1,23 @@
+.code
+
+UART_TX = $efe6
+UART_RX = UART_TX
+UART_STATUS = $efe7
+UART_CONTROL = UART_STATUS
+
+main:
+    ldx #$00
+loop:
+    lda UART_STATUS ; see if bit 0 is set
+    bit #$01
+    beq loop
+    lda UART_RX     ; read rx buffer if so
+    sta UART_TX     ; transmit it back again
+    bra loop
+
+
+.segment "VECTORS"
+
+.addr main
+.addr main
+.addr main