ANDROID: 16K: Init page_shift param in a pure_initcall()

Previously, page_shift_compat_enabled was initialized in the
early_param() function for page_shift. However, if page_shift
is passed as a bootconfig, page_shift_compat_enabled is not
initialized because it is too late.

In order to initialized page_shift_compat_enabled when
page_shift is passed as a kernel command line or bootconfig
parameter, a pure_initcall() will be used.

Bug: 376901009
Test: atest Vts16KPageSizeTest
Change-Id: I8127566062c5e0177636f2164a29801a0579ac51
Signed-off-by: Juan Yescas <jyescas@google.com>