platform/x86: mlx-platform: Move regmap initialization before all drivers activation

Initialize regmap prior drivers starting to allow passing regmap handle
to 'i2c_mlxcpld' driver.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>