s390x: use "lghi" for immediate values to fix build with clang

s390x: use "lghi" for immediate values to fix build with clang

Some of the kernels written in assembly utilize a "load address"
instruction for loading an immediate value into a register. That is
both unnecessarily complex and LLVM's assembler does not understand that
specific syntax. Thus, replace with the appropriate "load immediate"
instruction, which is also clearer to read.

Signed-off-by: Marius Hillenbrand <mhillen@linux.ibm.com>