Use 64-bit math when finding a block of ram to hold the kernel. This fixes
a problem on 32-bit systems which have ram occupying the end of the physical
address space -- for example, a block of ram at 0x80000000 with a size of
0x80000000 was overflowing 32 bit math and ending up with a calculated size
of zero.

This is a fix for one of the two problems mentioned in the PR. Something
similar will need to be done on the kernel side before the PR is closed.

PR: 201614