sunxi: remove __packed from struct sunxi_prcm_reg

struct sunxi_prcm_reg is naturally packed. There is no need to define it as
packed. Defining it as packed leads to compilation errors with GCC 9.2.1:

  CC      arch/arm/lib/reloc_arm_efi.o
arch/arm/cpu/armv7/sunxi/psci.c: In function ‘sunxi_cpu_set_power’:
:qarch/arm/cpu/armv7/sunxi/psci.c:163:21: error: taking address of packed
member of ‘struct sunxi_prcm_reg’ may result in an unaligned pointer value
[-Werror=address-of-packed-member]
  163 |  sunxi_power_switch(&prcm->cpu_pwr_clamp[cpu], &prcm->cpu_pwroff,
      |                     ^~~~~~~~~~~~~~~~~~~~~~~~~

Remove __packed attribute from struct sunxi_prcm_reg.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>