Add GetBlockDevSize, GetBlockDevSectors helpers

Helpers to get a block device size in bytes or 512 byte sectors,
using BLKGETSIZE64 and returning value of uint64_t type.

This also removes get_blkdev_size().

Test: build, manual, mount exFAT volume
Bug: 80202067
Change-Id: Ib07e8ac6ef7ff49de0ed570d1fa202e8b558b80c
diff --git a/model/Disk.cpp b/model/Disk.cpp
index 13cb1c7..2b6773d 100644
--- a/model/Disk.cpp
+++ b/model/Disk.cpp
@@ -243,12 +243,8 @@
     mSize = -1;
     mLabel.clear();
 
-    int fd = open(mDevPath.c_str(), O_RDONLY | O_CLOEXEC);
-    if (fd != -1) {
-        if (ioctl(fd, BLKGETSIZE64, &mSize)) {
-            mSize = -1;
-        }
-        close(fd);
+    if (GetBlockDevSize(mDevPath, &mSize) != OK) {
+        mSize = -1;
     }
 
     unsigned int majorId = major(mDevice);