lantiq: Fix build after kernel 5.15.150

This fixes the following compile problem:
````
  CC      arch/mips/kernel/vpe-mt.o
arch/mips/kernel/vpe-mt.c: In function 'vpe_run':
arch/mips/kernel/vpe-mt.c:32:23: error: unused variable 'physical_memsize' [-Werror=unused-variable]
   32 |         unsigned long physical_memsize = 0L;
      |                       ^~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[6]: *** [scripts/Makefile.build:289: arch/mips/kernel/vpe-mt.o] Error 1
````

physical_memsize was removed from upstream kernel, see:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.15.y&id=5b4f6c5ff65c8551018ccea40c569afd759734c0

Fixes: 387fde0da0e8 ("kernel: bump 5.15 to 5.15.150")
Signed-off-by: Hauke Mehrtens <[email protected]>

target/linux/lantiq/patches-5.15/0152-lantiq-VPE.patch

@@ -67,15 +67,7 @@ Signed-off-by: Stefan Koch <[email protected]>
  #endif /* _ASM_VPE_H */
 --- a/arch/mips/kernel/vpe-mt.c
 +++ b/arch/mips/kernel/vpe-mt.c
-@@ -29,6 +29,7 @@ int vpe_run(struct vpe *v)
- 	struct vpe_notifications *notifier;
- 	unsigned int vpeflags;
- 	struct tc *t;
-+	unsigned long physical_memsize = 0L;
- 
- 	/* check we are the Master VPE */
- 	local_irq_save(flags);
-@@ -415,6 +416,8 @@ int __init vpe_module_init(void)
+@@ -415,6 +415,8 @@ int __init vpe_module_init(void)
  			}
  
  			v->ntcs = hw_tcs - aprp_cpu_index();
@@ -84,7 +76,7 @@ Signed-off-by: Stefan Koch <[email protected]>
  
  			/* add the tc to the list of this vpe's tc's. */
  			list_add(&t->tc, &v->tc);
-@@ -518,3 +521,47 @@ void __exit vpe_module_exit(void)
+@@ -518,3 +520,47 @@ void __exit vpe_module_exit(void)
  			release_vpe(v);
  	}
  }

target/linux/lantiq/patches-5.15/0155-lantiq-VPE-nosmp.patch

@@ -10,7 +10,7 @@ Signed-off-by: Stefan Koch <[email protected]>
 
 --- a/arch/mips/kernel/vpe-mt.c
 +++ b/arch/mips/kernel/vpe-mt.c
-@@ -131,7 +131,10 @@ int vpe_run(struct vpe *v)
+@@ -130,7 +130,10 @@ int vpe_run(struct vpe *v)
  	 * kernels need to turn it on, even if that wasn't the pre-dvpe() state.
  	 */
  #ifdef CONFIG_SMP