xen/arm: Drop early_uart_init macro from debug-meson.inc

early_uart_init macro is only used if CONFIG_EARLY_UART_INIT is set.
This config option depends on EARLY_UART_PL011, so there is no point
in defining it for MESON, especially if it is empty. Remove it and adapt
the existing comment.

Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Acked-by: Julien Grall <julien@xen.org>

xen/arch/arm/arm64/debug-meson.inc

@@ -23,9 +23,10 @@
 
 #define AML_UART_TX_FIFO_FULL   21
 
-.macro early_uart_init xb, c
-/* Uart has already been initialized by Firmware, for instance by TF-A */
-.endm
+/*
+ * No need for early_uart_init, as UART has already been initialized
+ * by Firmware, for instance by TF-A.
+ */
 
 /*
  * MESON UART wait UART to be ready to transmit