soc/mediatek/mt8188: Decrease OP-TEE image size from 80 MB to 70 MB

The secure buffer shrank from 42 MB to 32 MB, decreasing the total
OP-TEE image size from 80 MB to 70 MB.

BUG=b:246837563
TEST=emerge-geralt coreboot
     build coreboot and verify SVP works well

Change-Id: I6729e65f83ef994fe59b5bd4ed098e6d3a847695
Signed-off-by: Gavin Liu <gavin.liu@mediatek.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82634
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yidi Lin <yidilin@google.com>
Reviewed-by: Eric Lai <ericllai@google.com>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>

src/soc/mediatek/mt8188/soc.c

@@ -15,7 +15,7 @@
 #include <symbols.h>
 
 #define OPTEE_ADDRESS		0x43000000
-#define OPTEE_SIZE		(80 * MiB)
+#define OPTEE_SIZE		(70 * MiB)
 
 void bootmem_platform_add_ranges(void)
 {