[IA64] pvops: preparation: move the constants, LOAD_OFFSET, to a header file.

Move the LOAD_OFFSET definition from vmlinux.lds.S into system.h.
On paravirtualized environments, it is necessary to detect the
execution environment. One of the solutions is the multi entry point.
The multi entry point allows a boot loader to start the kernel execution
from the entry point which is different from the ELF entry point.
The non standard entry point will defined as the specialized elf note
which contains the LMA of the entry point symbol.
The constant, LOAD_OFFSET, is necessary to calculate the symbol's LMA.
Move the definition into the public header file to make it available
to the multi entry point support.

Cc: "He, Qing" <qing.he@intel.com>
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Tony Luck <tony.luck@intel.com>