board/qemu/aarch64-sbsa: use the default console specified by ACPI

ARM SBBR (Server Base Boot Requirements) defines SPCR (Serial Port
Console Redirection Table) as a mandatory ACPI table that specifies
the configuration of a serial console.

In the linux kernel, ARM developers have decided that consoles defined
by SPCR are always enabled when existing, see e.g.:
https://lore.kernel.org/linux-serial/20200430161438.17640-1-alpernebiyasak@gmail.com/T/

Specifying console=ttyAMA0 (which is a serial console) is thus
redundant for an ARM SBSA board. (It also blindly assumes that
the serial console is on ttyAMA0, which might not be true.)

Drop the explicit console=ttyAMA0 on the kernel command line,
such that the kernel can pick up the default console defined
by SPCR.

This is similar to how it is currently done for
board/aarch64-efi/grub.cfg.

Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

board/qemu/aarch64-sbsa/grub.cfg

@@ -2,5 +2,5 @@ set default="0"
 set timeout="5"
 
 menuentry "Buildroot" {
-	linux /Image root=PARTLABEL=root rootwait console=ttyAMA0
+	linux /Image root=PARTLABEL=root rootwait
 }