This patch moves BUG() and PAGE_BUG() from asm/page.h into asm/bug.h.

We also fix up linux/dcache.h, which included asm/page.h for the sole
purpose of getting the BUG() definition.

Since linux/kernel.h and linux/smp.h make use of BUG(), asm/bug.h is
included there as well.

In addition, linux/jbd.h did not contain a clear path with which to
obtain the archtecture BUG() definition, but did contain its own
definition.