kernel: bump 5.4 to 5.4.45

kernel: bump 5.4 to 5.4.45

Fixes CVE-2020-10757 via upstream commit df4988aa1c96 ("mm: Fix mremap
not considering huge pmd devmap").

Resolved merge conflict in the following patches:

 bcm27xx: 950-0128-gpiolib-Don-t-prevent-IRQ-usage-of-output-GPIOs.patch

Refreshed patches, removed upstreamed patch:

 generic: 751-v5.8-net-dsa-mt7530-set-CPU-port-to-fallback-mode.patch
 generic: 754-v5.7-net-dsa-mt7530-fix-roaming-from-DSA-user-ports.patch

Run tested: qemu-x86-64
Build tested: x86/64, imx6, sunxi/a53

Signed-off-by: Petr Štetiar <ynezz@true.cz>