x86/platform/UV: Mark memblock related init code and data correctly

parse_mem_block_size() and mem_block_size are only used during init. Mark
them accordingly.

Fixes: d7609f42 ("x86/platform/UV: Add kernel parameter to set memory block size")
Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: hpa@zytor.com
Cc: Mike Travis <mike.travis@hpe.com>
Cc: Andrew Banman <andrew.banman@hpe.com>
Link: https://lkml.kernel.org/r/20180730075947.23023-1-douly.fnst@cn.fujitsu.com