fat: Enable 4096-byte sector sizes

* Correct code that only works when sector size is 512 bytes.
* For devices with 4096-byte sectors, use 4096 as the size of blocks
  in the block cache, and as the unit of IO requests in FAT
  operations.
* Some values continue to be stored in 512-byte units, regardless of
  sector size, in keeping with the original BSD driver.
* Fixes #19686.

Change-Id: I8fa77aeab1bc93a5465134018c3113afb2a80b8b
Reviewed-on: https://review.haiku-os.org/c/haiku/+/9542
Reviewed-by: waddlesplash <[email protected]>

headers/private/fs_shell/fssh_kernel_priv.h

@@ -46,6 +46,7 @@
 
 #define ROUNDUP(a, b) (((a) + ((b)-1)) & ~((b)-1))
 #define ROUNDDOWN(a, b) (((a) / (b)) * (b))
+#define HOWMANY(a, b)	(((a) + ((b) - 1)) / (b))
 
 
 #define CHECK_BIT(a, b) ((a) & (1 << (b)))