ANDROID: KVM: Include prototype for page_relinquish before definition

Fixes build failure on -Werror=missing-prototypes.

At the same time, make the header file more resilient to ordering by
declaring 'struct page'.

Bug: 240239989
Change-Id: I84d069bde5ff03d1afa55d25c01448b0d43042da
Signed-off-by: Keir Fraser <keirf@google.com>

arch/arm64/include/asm/mem_relinquish.h

@@ -7,6 +7,8 @@
 #ifndef __ASM_MEM_RELINQUISH_H
 #define __ASM_MEM_RELINQUISH_H
 
+struct page;
+
 void page_relinquish(struct page *page);
 
 #endif	/* __ASM_MEM_RELINQUISH_H */

arch/arm64/mm/mem_relinquish.c

@@ -5,6 +5,7 @@
  */
 
 #include <linux/arm-smccc.h>
+#include <linux/mem_relinquish.h>
 #include <linux/memory.h>
 #include <linux/mm.h>
 #include <linux/types.h>