drivers: serial: Add xtensa semihosting driver

Add xtensa semihosting driver.

It can't use regular semihosting driver as Xtensa's has it's own
semihosting ABI.

Tested-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
diff --git a/drivers/serial/Makefile b/drivers/serial/Makefile
index dbe598b..78810f9 100644
--- a/drivers/serial/Makefile
+++ b/drivers/serial/Makefile
@@ -60,6 +60,7 @@
 obj-$(CONFIG_HTIF_CONSOLE) += serial_htif.o
 obj-$(CONFIG_SIFIVE_SERIAL) += serial_sifive.o
 obj-$(CONFIG_XEN_SERIAL) += serial_xen.o
+obj-$(CONFIG_XTENSA_SEMIHOSTING_SERIAL) += serial_xtensa_semihosting.o
 obj-$(CONFIG_S5P4418_PL011_SERIAL) += serial_s5p4418_pl011.o
 
 ifndef CONFIG_SPL_BUILD