ipq806x: disable SPC of IPQ8064 on NEC WG2600HP to fix boot issue

ipq806x: disable SPC of IPQ8064 on NEC WG2600HP to fix boot issue

The SPC (Standalone Power Collapse) of IPQ8064 on NEC Aterm WG2600HP
need to be disabled to fix the boot stucking issue on WG2600HP with
kernel 5.4.

log:

[    3.036965] cpuidle: enable-method property 'qcom,kpss-acc-v1' found operations
[    3.038007] cpuidle: enable-method property 'qcom,kpss-acc-v1' found operations
[    3.045849] sdhci: Secure Digital Host Controller Interface driver
[    3.052385] sdhci: Copyright(c) Pierre Ossman
[    3.058712] sdhci-pltfm: SDHCI platform and OF driver helper
[    3.065469] NET: Registered protocol family 10
[    3.070184] Segment Routing with IPv6
[    3.073141] NET: Registered protocol family 17
[    3.078157] 8021q: 802.1Q VLAN Support v1.8
[    3.081149] Registering SWP/SWPB emulation handler
[    3.107125] qcom_rpm 108000.rpm: RPM firmware 3.0.16777371
[    3.120475] s1a: Bringing 0uV into 1050000-1050000uV
[    3.120747] s1a: supplied by regulator-dummy
[    3.124775] s1b: Bringing 0uV into 1050000-1050000uV
[    3.128969] s1b: supplied by regulator-dummy
[    3.133905] s2a: Bringing 0uV into 800000-800000uV
[    3.138190] s2a: supplied by regulator-dummy
[    3.142693] s2b: Bringing 0uV into 800000-800000uV
[    3.147266] s2b: supplied by regulator-dummy
[
(stuck)

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>