kernel: copy kernel 4.19 code to 5.4

No changes were done to the patches while coping them. Currently they do
not apply on top of kernel 5.4.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/generic/pending-5.4/307-mips_highmem_offset.patch

@@ -0,0 +1,19 @@
+From: Felix Fietkau <nbd@nbd.name>
+Subject: kernel: adjust mips highmem offset to avoid the need for -mlong-calls on systems with >256M RAM
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+ arch/mips/include/asm/mach-generic/spaces.h | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+--- a/arch/mips/include/asm/mach-generic/spaces.h
++++ b/arch/mips/include/asm/mach-generic/spaces.h
+@@ -50,7 +50,7 @@
+  * Memory above this physical address will be considered highmem.
+  */
+ #ifndef HIGHMEM_START
+-#define HIGHMEM_START		_AC(0x20000000, UL)
++#define HIGHMEM_START		_AC(0x10000000, UL)
+ #endif
+ 
+ #endif /* CONFIG_32BIT */