power: pfuze100 correct SWBST macro definition

According to datasheet, SWBST_MODE starts from bit 2 and it occupies 2 bits.
So SWBST_MODE_MASK should be 0xC, and SWBST_MODE_xx should be ([mode] << 2).

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Cc: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Stefano Babic <sbabic@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>