asm-generic: global_data: change timebase_l/h to unsigned int

Change type of timebase_l/h to unsigned int.
>From lib/time.c: ((uint64_t)gd->timebase_h << 32) | gd->timebase_l;
This piece code is based on that timebase_h and timebase_l are
32bits width, so change the type to unsigned int.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Eddie Cai <eddie.cai.linux@gmail.com>
Cc: Jagan Teki <jteki@openedev.com>
Cc: York Sun <york.sun@nxp.com>
Cc: "Robert P. J. Day" <rpjday@crashcourse.ca>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>