drivers: partition: support different block size

The block size of some storage device is 4096-byte long, such as UFS. But
PARTITION_BLOCK_SIZE is defined as 512-byte long. So replace it by
PLAT_PARTITION_BLOCK_SIZE. Make it configurable in platform.

Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>
Change-Id: Iada05f7c646d0a0f2c0d3b8545540b3cb7153de3
diff --git a/drivers/partition/gpt.c b/drivers/partition/gpt.c
index 4577f06..1b804de 100644
--- a/drivers/partition/gpt.c
+++ b/drivers/partition/gpt.c
@@ -52,9 +52,10 @@
 	if (result != 0) {
 		return result;
 	}
-	entry->start = (uint64_t)gpt_entry->first_lba * PARTITION_BLOCK_SIZE;
+	entry->start = (uint64_t)gpt_entry->first_lba *
+		       PLAT_PARTITION_BLOCK_SIZE;
 	entry->length = (uint64_t)(gpt_entry->last_lba -
 				   gpt_entry->first_lba + 1) *
-			PARTITION_BLOCK_SIZE;
+			PLAT_PARTITION_BLOCK_SIZE;
 	return 0;
 }