Add usage flags for old gralloc

vkgetSwapchainGrallocUsageANDROID() now sets
a single flag to GRALLOC_USAGE_SW_WRITE_OFTEN

Bug: b/122837237
Change-Id: I809659c6bbc49b84302b8c58751de5ed0135b1ef
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/32249
Tested-by: Hernan Liatis <hliatis@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>

src/Vulkan/libVulkan.cpp

diff --git a/src/Vulkan/libVulkan.cpp b/src/Vulkan/libVulkan.cpp
index 5b0690f..396e2f2 100644
--- a/src/Vulkan/libVulkan.cpp
+++ b/src/Vulkan/libVulkan.cpp
@@ -2770,6 +2770,8 @@
 	TRACE("(VkDevice device = %p, VkFormat format = %d, VkImageUsageFlags imageUsage = %d, int* grallocUsage = %p)",
 			device, format, imageUsage, grallocUsage);
 
+	*grallocUsage = GRALLOC_USAGE_SW_WRITE_OFTEN;
+
 	return VK_SUCCESS;
 }