platform/x86: dell-laptop: Allocate buffer on heap rather than globally

platform/x86: dell-laptop: Allocate buffer on heap rather than globally

There is no longer a need for the buffer to be defined in
first 4GB physical address space.

Furthermore there may be race conditions with multiple different functions
working on a module wide buffer causing incorrect results.

Fixes: 9affb643aebaeb4573868d57e37e638c71bb1ff3
Suggested-by: Pali Rohar <pali.rohar@gmail.com>
Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>