[ARM] i.MX6 clocking code calls to Xvisor API corrected.

The 'vmm_sprintf' function does not return an error code, but the number of
buffer written bytes.
The 'vmm_printf', called through 'pr_err', does not support the '%ld', as 'l'
is not a length modifier, but a conversion specifier.
[DRIVER] i.MX6 serial warning corrected.

A warning on a bitwise OR operation has been corrected.
[ARM] i.MX6 CCM device added in the device tree, required for LP clocking.

As the CCM was not declared in the device tree, the associated driver, in
arch/arm/cpu/board/common/imx/clk-imx6q.c was not initialized. Thus, the Low
Power Manager clocking did not set the low power wait mode as clocked, state in
which a WFI set the processor to. In consequence, when the first proc_do_idle
was called, the JTAG probe lost its control over the processor.
The scheduling was functioning though, as the EPIT timer was running.