kboot: Implement munmap(2)

Define host_munmap so we can use it in the x86 code to find things for
the BIOS/CMS boot path and unmap after we find it.

Sponsored by:		Netflix

stand/kboot/arch/amd64/syscall_nr.h

@@ -4,6 +4,7 @@
 #define SYS_kexec_load		246
 #define SYS_lseek		  8
 #define SYS_mmap		  9
+#define	SYS_munmap		 11
 #define SYS_newfstat		  5
 #define SYS_newfstatat		262
 #define SYS_openat		257

stand/kboot/arch/powerpc64/syscall_nr.h

@@ -5,6 +5,7 @@
 #define SYS_kexec_load		268
 #define SYS_llseek		140
 #define SYS_mmap		 90
+#define	SYS_munmap		 91
 #define SYS_newfstat		SYS_fstat
 #define SYS_newfstatat		291
 #define SYS_openat		286

stand/kboot/host_syscall.h

@@ -96,6 +96,7 @@ int host_gettimeofday(struct host_timeval *a, void *b);
 int host_kexec_load(uint32_t start, int nsegs, uint32_t segs, uint32_t flags);
 ssize_t host_llseek(int fd, int32_t offset_high, int32_t offset_lo, uint64_t *result, int whence);
 void *host_mmap(void *addr, size_t len, int prot, int flags, int fd, off_t off);
+int host_munmap(void *addr, size_t len);
 int host_open(const char *path, int flags, int mode);
 ssize_t host_read(int fd, void *buf, size_t nbyte);
 int host_reboot(int, int, int, uintptr_t);

stand/kboot/host_syscalls.c

@@ -57,6 +57,12 @@ host_mmap(void *addr, size_t len, int prot, int flags, int fd, off_t off)
 	return (void *)host_syscall(SYS_mmap, (uintptr_t)addr, len, prot, flags, fd, off);
 }
 
+int
+host_munmap(void *addr, size_t len)
+{
+	return host_syscall(SYS_munmap, (uintptr_t)addr, len);
+}
+
 int
 host_open(const char *path, int flags, int mode)
 {