module/gtimer: add new flag for CNTCONTROL register initialization

The CNTCONTROL register is accessible by secure accesses only. So, add a
new flag to enable/disable the CNTCONTROL register initialization.

This is used by control processors like MCP to configure the timer only
since it does not generate secure transactions and hence cannot
configure this register.

Signed-off-by: Shriram K <shriram.k@arm.com>
Change-Id: Iada7130e1355c94295c536bd8a62f17b582b00d1