psp_verstage: make get_max_workbuf_size optional

From cezanne we have enough space in PSP so we don't have to worry about
workbuf size. Hence the function only exists in picasso and deprecated
for later platforms.

So wrap svc_get_max_workbuf_size and provide default weak function so
future platforms don't have to implement dumb function for it.

TEST=build and boot zork, check weak function is not called in zork

Signed-off-by: Kangheui Won <khwon@chromium.org>
Change-Id: I16e8edf8070aaacb3a6a6a8adc92b44a230c3139
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52687
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/soc/amd/picasso/psp_verstage/svc.c

@@ -149,6 +149,11 @@ uint32_t svc_write_postcode(uint32_t postcode)
 	return retval;
 }
 
+uint32_t get_max_workbuf_size(uint32_t *size)
+{
+	return svc_get_max_workbuf_size(size);
+}
+
 uint32_t svc_get_max_workbuf_size(uint32_t *size)
 {
 	uint32_t retval = 0;