imx: syscounter: allow timer_init for SPL build

imx: syscounter: allow timer_init for SPL build

With enabled SKIP_LOWLEVEL_INIT, the weak function timer_init() is
used in the SPL build. For iMX6 SoC, this leads MMC to fail once
u-boot proper is booted due to a timing issue.
Always use iMX-specific timer_init() in SPL to fix timing issues.

Fixes: be277c3a89 ("imx: mx7: avoid some initialization if low level is skipped")
Signed-off-by: Michael Scott <mike@foundries.io>
Co-developed-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
Reviewed-by: Peng Fan <peng.fan@nxp.com>