ARM: at91: pm: use r7 instead of tmp1

Use r7 instead of tmp1 in macros. This prepares the filed for
next commits.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20210415105010.569620-7-claudiu.beznea@microchip.com