Set PROT_EXEC on the whole pixelflinger code cache.

The pointer difference between word pointers is a number
of words, and it needs to be multiplied by the size of a word
to get a proper byte size.

Without this, we tend to see crashes when the code crosses
a page boundary.

Bug: 3026204
Bug: 3097482
Change-Id: I37776d26d5afcdb1da71680de02fbb95e6548371

libpixelflinger/codeflinger/CodeCache.cpp

@@ -94,7 +94,7 @@ void Assembly::ensureMbaseExecutable()
     long pagemask = ~(pagesize - 1);  // assumes pagesize is a power of 2
 
     uint32_t* pageStart = (uint32_t*) (((uintptr_t) mBase) & pagemask);
-    size_t adjustedLength = mBase - pageStart + mSize;
+    size_t adjustedLength = (mBase - pageStart) * sizeof(uint32_t) + mSize;
 
     if (mBase && mprotect(pageStart, adjustedLength, PROT_READ | PROT_WRITE | PROT_EXEC) != 0) {
         mspace_free(getMspace(), mBase);